After Effects CS4

PDF (adobe.com)

Drawing, painting, and paths

Creating shapes and masks

Creating masks
Create a rectangular or elliptical mask numerically
Create a mask from a channel with Auto-trace
Creating shapes and shape layers
Create a shape or mask by dragging with shape tools
Create a Bezier shape or mask using the Pen tool
Create a shape or mask the size of the layer
Create shapes or masks from text characters
Copy a path from Illustrator, Photoshop, or Fireworks
Create a mask or shape from a motion path

community help (adobe.com)