In request, I decided to create a sort of beginner's guide to Payday 2. I'll try to spread this out over several posts and probably several days, but I'd like start where you would if you just picked up the game, or if you'd never played it before: The very basics.
So you just launch Payday 2 for the first time?
Go into Options menu under Video -> Advanced and adjust your FOV slider to the maximum the game will allow. The default FOV (Field Of View) in Payday 2 is very, very low. What this means is you have next to no peripheral vision. This has the effect of making you almost blind to enemies coming in on your side and can cause some people to feel motion sick. There are other options to mess with there, but this is the one that you WANT to max out as soon as possible.
Once that's done, hit the "Safe House" option. This is your tutorial and it'll introduce you to the basics of the game. Don't worry about Skill or Inventory for the moment - you very likely can't do anything there yet, anyway. Once in the Safe House, a voice will talk at you over the radio. This is "Bain" and he'll be your mission control for the rest of the game. He'll teach you how to pick up and drop bags (a central mechanic of the game) as well as how to use guns. Eventually he'll let you into the basement and essentially leave you on your own. Don't end the tutorial yet. Explore the basement first. You'll find four rooms. Straight ahead from the staircase is your vault. This is where your money will stack up once you have any. The rest of the rooms I'll make into minor tutorials of their own.
Left of the staircase is a room with a bunch of closed doors secured to a makeshift wooden frame. You can walk around the doors and get to the other side, but that's not the point. This area is there to teach you how to open the doors themselves, as well as what kind of doors there are in the game. Generally speaking, there are three kinds of doors: weak doors, strong doors and security doors. You have examples of all three kinds in the room.
Weak doors are made of wood. You can pick their locks by hand without any skills necessary, and it'll take you 10 seconds to do so. Alternately, you can "breech" them by shooting the lock off with any firearm. Contrary to what NT might say, this is the preferred method for opening these doors. However, you may notice that you keep shooting the doors and nothing happens. This is because the locks have a certain amount of "hit points" that you have to deplete. With a shotgun that usually goes in a single hit but most other weapons will take multiple shots. You should also note that the game is very... Particular about where it wants you to shoot the door for the shots to count. You want to aim for the door handle/knob for best return on investment. While weak doors are usually made of wood, they also include glass doors with metal frames. Most of the doors in the "door room" are weak doors.
Strong doors are made of metal. You can pick their locks by hand without any skills necessary, but it'll take you 20 seconds to do so. Strong doors cannot be shot open with any actual weapons (not even the grenade launcher) but can be sawed open with the OVE9000 Saw. This is a high-level skill in the Enforcer tree, so I'll discuss it another time. For now, just assume that you need to pick the locks on those, and that it'll take you a long time. Strong doors almost always take the form of a featureless flat white metal door with a chrome door knob.
Security doors are marked with a GenSec sticker and have a keycard reader next to them. Security doors cannot be picked in any way, since they don't have a lock. The lock itself can be overridden with an ECM (low-level Ghost skill) or cut with an OVE9000 Saw. Assuming you don't have either - which is usually the case - you have two options to open these doors: Keycard or Drill. There's a keycard on the table in the training area so you know what it looks like. You can only carry one keycard at a time, and it's consumed when you use it. What this means is if you need to open multiple security doors, you'll have to pick which one to open. Failing that, you need to drill the door. The Payday gang have an infinite supply of automatic drills. Just interact with the drill symbol to place one on the door, then wait until the drill finishes. I'll talk more about drills in particular later.
Once you've had your fun opening doors, leave the room.
Guns, guns, guns!
Right of the staircase is a corridor with two rooms on the side. The first one is your firing range. The antechamber to the actual range holds racks where your guns and masks will be showcased once you have a few. The actual gun range is about the only reason to keep going back to your safehouse even after the tutorial is done. Hit the button on the wall to listen to Bain babble about nothing in particular and that'll activate the pop-up targets. Deal enough damage and they'll go down. Knock them down enough times and the next row farther down the line will pop up. If you run out of ammo, two ammo bags are provided for you to restock. But let's talk about weapon mechanics.
Guns in Payday work in an attempt at a semi-realistic fashion. Simply pressing the fire button will fire your gun "from the hip." While you have no on-screen crosshair when firing from the hip, your gun is still aimed at the centre of the screen. Laser sights (I'll explain later) can help show where that is. If you want to shoot accurately, you need to "aim down sights" (hold right mouse button by default), which will bring the weapon up to your face. By default, most weapons (with one exception) will use iron sights for aiming. I find this almost impossible to use, however, and would advise acquiring a scope as soon as possible, but more on scopes in a bit.
As you can imagine, most guns have their own accuracy. Here this constitutes a circle around your aim direction. Any shot you fire has a chance to land anywhere in that circle. Accuracy varies depending on how you shoot. Though this varies by the specific guns, a rough set of rules goes like this: Firing from the hip and firing while moving make you less accurate. Firing while aiming, firing while stationary and sometimes firing while crouching improve your accuracy. Accuracy also degrades as you fire in longer bursts, meaning your first few shots will be more accurate. To preserve accuracy and save ammo, fire in short, controlled bursts.
Weapon recoil is also a very real thing, and many weapons in the game can kick like a mule. Recoil here is represented by your aim shifting in a random direction away from where you're actually aiming with every shot you fire. Most guns kick up and pull to the right, but this isn't always the case. Usually, you can compensate for this by pulling your mouse against the recoil to recentre your aim, but this kills your ability to shoot straight, as you can imagine. Recoil can be mitigated with weapon mods, but only up to a point. Every single weapon in Payday 2 kicks to some degree. If you want to play this game, you need to learn to handle the kick.
Safes and drills
Past the firing range a room which showcases a number of safes you'll run across in the game. Generally speaking, they come in three sizes - small, tall and fat. There's no real mechanical difference between them. They only differ in how long they take to drill through and how much loot can be in them. In addition to drilling them, safes can be lockpicked but ONLY if you have Lockpick skill (high-level Ghost skill), as well as blown up with shaped charges (high-level Technician skill). Not featured in this room are Titan safes. These are much stronger and sport electronic locks. The only real difference there is Titan safes cannot be lockpicked or blown up. You HAVE to drill them.
Now seems like a good time to talk about "drills," for they are central to Payday 2. Indeed, it's been called a "drilling simulator." Almost every major objective in the game requires you to drill something, be it a door, a safe or something esoteric like a SWAT van. To do this, you need to interact with the object, which attackes a portable, automatic drill. The drill comes with an LCD on the side which tells you how long it'll be before it finishes. Don't be shocked if you see upwards of 200 seconds - drills in this game are slow. Payday 2 is, to a large extent, a horde defence games and drills are the game's way of enforcing this. They take a long time and you need to not just defend them but also manage them.
Every single drill you place no matter your luck will break on its own AT LEAST once. When this happens, it'll make a continuous distinct sound, the characters will never shut up about fixing it and the LCD will display "Error." Simply interact with the drill to fix it, though keep in mind this is a slow process and takes about 20 seconds. Drills can break on their own several times, but cops can also break them. When this happens, you need to clear the area around the drill and restart it as normal. Don't leave your drills unguarded if you can manage it. Having to fix a 5-minute drill every 30 seconds can slow you down tremendously.
You have an infinite supply of normal drills in your bag of holding and you can place as many of them there are things to drill. There are literally no limits to this. However, certain missions will require you to use a "thermal drill." For all intents and purposes, that's just a larger version of the regular drills which actually takes the form of a bag when not deployed. Thermal drills are used to drill bank vaults, so you need to bring the bag to the vault before you can start the drill. Past that, it behaves exactly like a regular drills. Both Thermal drills and regular drills can benefit from a number of Technicial skills.
Guys, the Thermal Drill! Go get it!
Cameras and guards
At the end of the hallway right of the staircase is a desk with a console at it. This is hooked up to the building's security cameras. Familiarise yourself with the controls, since this will come in handy in the actual game. You can flip through the various cameras with your fire and aim buttons (left an right mouse by default), you can zoom in with your forward and backward movement keys and you can leave the camera view with your jump key.
Cameras are useful for two distinct functions. For one, they help you get a better view of locations which might be difficult to observe directly, such as the interior of a bank that you can't get into yet. More importantly, however, is that cameras "mark" guards in stealth and special cops during a firefight. "Marked" enemies appear in red outline that's visible through walls and from very far away. This helps warn your team-mates of danger and give them better situational awareness.
I'd say more, but since cameras are mostly useful in stealth, I'll save that for when I talk about stealth.
You're done here
Once you've explored all the rooms in the Safe House, return to the staircase and interact with the laptop. That'll end the tutorial and return you to the main menu.