How do you record video in photo booth?

In the bottom-left corner of the Photo Booth window, just above the slides where it shows all your recent pictures, there are three buttons.

The first is to take a single picture.
The second will take a sequence of four pictures.
The third will record movies from your iSight camera!

Open Photo Booth. In the left hand corner below the image window are three buttons. The third button is used to take a video clip.