The Outpost

Start by turning around and then moving forward.  You'll find a stash of supplies with an MP5, ammunition, and flares.  Collect these items and then enter the outpost.  Move through the outpost and you'll eventually reach your first couple of squad mates and receive some input on their skills.

In the room that you are in, you'll see a broken electrical box.  Turn to your engineer and have him fix the box for you.  Once he fixes the box, a door will open.  After you pass through the door, an explosion will occur and you'll take some damage.  Have your medic heal you and restore your health.

After you've been healed, collect the weapons and ammo that you find in the room.  Give away some of the weapons and ammo to your squad mates in order to build their trust for you.

Leave the room and head back towards the entry hallway.  An explosion will then clear some debris and open a new pathway for you.  Follow the new pathway and you'll eventually exit the building.  You'll first pass through a destroyed room and come across a locked door.  The game will then inform you that you need to gain access to this room.

Follow the light posts until you reach an excavated pit.  Follow the ramp down into the pit and you'll find a fire extinguisher and some flares.  As you continue exploring the pit you'll come across a shack.. enter the shack and play the tape recorded message for a movie reference.  Exit the shack and continue across the pit and you'll come to a tunnel that leads to the excavation of the alien spacecraft.  You'll find the key to the infirmary sitting on a table in this area.

Return to the infirmary, open the door, and enter the next room.  On your left you will find a malfunctioning electrical box - order your engineer to repair it.  There is a door near the box that requires you to enter an access code to pass.  The access code for the door is stored on the computer you'll find in the room.

Enter the code that you found to pass through the secure door.  In the next room you'll find a medkit with health packs and another malfunctioning electrical box for your engineer to fix.  Once this box is fixed, you'll be able to pass through the next door and save your game on the recorder.

Exit through the door that leads to the outside.  Again you'll need to follow the light posts and they'll lead you to a small shack.  Once inside the shack, you'll discover a body and initiate a cutscene in which you'll be instructed to destroy the outpost with C4.

Exit the shack and follow the new path illuminated by light posts.  These light posts will eventually lead you to a helicopter wreck with a crate of C4 nearby.  Take the C4.

Follow the light poles back to base, and return to the infirmary.  You'll see an outline of a C4 charge that will let you know where to place your first C4 charge.  A similar outline will appear in the radio room, and you'll need to place the second charge there.  Once both charges have been placed, return to the location where you obtained the C4 charges in the first place and your team will be extracted.