Gears of War/Act One: Ashes

Find Another Way Out
Here is where you first encounter a Berserker. She kills one of the Alpha Squad soldiers that was the one path out, so you have to find another way out.

Lure The Berserker Outside
With the Berserker on the chase, you must lure it outside so you can use The Hammer of Dawn on her. You have only seven minutes of satellite coverage for The Hammer of Dawn so make good use of that time.

Run to smashable door, face the Berserker, and wait for her to charge at you. When she is very close, just walk sideways, and she will run past you, breaking the door.

This will have to be repeated a few times as you will travel room to room with the Berserker chasing after you. Lure her towards the doors and she will bust through them.

Kill The Berserker
Once you are outside, get some good distance on her and wait. Once she is in your sights use The Hammer of Dawn on her twice to finish the job.

Congrats, you have finished Act 1!

Continue the Single-Player Walkthrough in Act 2