As you exit the elevator, the computer tells you something rather ominous: the particle field that prevents you from bringing objects into the elevator to the next level can sometimes remove fillings and teeth, leaving the taste of blood in your mouth. This place is scary.
Anyway, when you reach the glass window, you will see something rotating in the middle of the room that is creating blue portals. Go through the chamber lock and down the stairs, and you will seem trapped, but just wait for a few moments. The rotating thing in the part of the room that you can't reach will shoot a blue portal onto the wall in this area. When it does, go through it.
Now you're up on a ledge, and you can hop down to the area with the rotating thing, or you can go through the orange portal when the rotating thing creates a blue one in that area.
Walk up to the rotating thing and you'll pick it up. The computer explains that the object is a portal gun. It creates blue portals. The computer assures you that portals have been proven to be completely safe, but the portal gun has not. She proceeds to list several warnings, and finishes by saying something like "under no circumstances" but then there's some sort of malfunction and you never find out what that warning is. Better just be careful then, I guess?
Anyway, now that you can create blue portals, create one on a nearby wall and walk through it. The chamber lock will be open now, and you can go into the elevator to the next level. Don't worry: the portal gun doesn't get destroyed when you go through the particle field.