The Geneva drive is a mechanical device that transform a smooth rotation into an intermittent rotary motion. Traditionally, this has had applications within watch making.
The Lego mechanism showcased here transfers one rotation of the drive axle into 1/4 rotation of the output axle. Here are the basic movements explained.
The driving axle (to the right) locks the output axle, due to the black half circle shape.
As the black half circle moved away and opens up for the output axle movement, the blue pin slides into the cross shaped contraption:
The blue pin rotates the output axle by 90°:
As the blue pin slides out of the cross shape, the black half circle again locks the output axle, so it remains stationary:
Here is a video illustrating how it runs:
Here is how to make the drive wheel:
And the driven wheel is made like this: