Deus Ex: Human Revolution/Welcome to the Revolution

You start out in Megan Reed's office, where you can do a little exploring before talking to her and triggering a long walk through the Sarif Industries lab on your way up to the boss' office. While talking with David Sarif about security for the upcoming conference, an alarm will sound and he'll send you down to investigate. Head to the elevator on the side of the room and punch in the code Sarif gave you: 0451. On the way down, Frank Pritchard will note that he's getting interference in the network from somewhere and it looks like Megan is running, so you'll be on high alert when you leave the elevator.

As you move through the labs looking for the source of the disturbance, follow the prompts to view short tutorials on game mechanic basics. You have a combat rifle for this segment, which will let you take out the enemies you encounter, or you can sneak by them if you want to avoid conflict or are trying for a non-lethal runthrough (or just run through, since they can't follow you from section to section). Remember to stay behind cover in a firefight and move when they can't see you.

Through the labs
Head down the first hallway and crouch to go under the security door. Proceed down the hallway until you see a lab tech behind some security glass. A large augmented man will drag another tech out of a side room and kill them both before walking away. Enter the room on the side and move the top crate stacked in front of the vent, exposing the way through to the other side. After exiting the air duct, go down the hall and through the doors to a lab. Get cover if you plan to shoot the enemies that appear, or run far into the lab on the right side for cover if you want to sneak by them. After they come down the stairs and start patrolling the lab, you can use either method to get up the stairs and out into the next hall.

At the end of the hallway are doors to another lab, this time with guards already inside. There is a large window in the hallway, so be careful the guards don't spot you as you make your way to the door. When you get there you can hear the guards talking. Take this time to open the lab door and either gun them down while they're not alerted, or go in and get cover behind the generator on the right if you want to sneak through. If you opted to shoot, take the three out, then move on, otherwise use the counter after the generator for cover and move up behind the stationary guard. When the other two aren't looking, you'll want to grab the trashcan and throw it back the way you came to distract him so you can get out unseen.

Down the next hall you'll find another augmented soldier killing scientists before a glass door opens for you into the next lab. This time you're at the top of some stairs and there are four guards. Start a firefight, or use cover to get down the stairs and take a left to behind the desks between you and the guards. You can go from cover to cover to the other side of the room and end up on the other side of the long counter in the center from the two stationary guards. Wait until no one's looking then, head through the burned out door to continue on. As you head down the hallway filled with burning debris, you'll encounter a third mech, this time dealing with your directly.

Note: Don't worry about wasting bullets. There's an infinite amount of ammo, although it will reload or you decide to reload during this mission.