The large elevator that brings you into the structure is labeled with the blue '1'. From here, you head down and through the door on the right, then through the next room into the hallway that acts as loading zone #1.
Watch the movie for Zone #1
On the other side of this hallway is a room with some rubble in the corner - use it to climb up to the upper level, and continue on to the movie cutscene. Once you've seen that, the doorway out of the first big room you get to leads to loading zone #2.
Watch the movie for Zone #2