The Mask effect cuts out a portion of an image using a matte drawing. You can use the Mask effect to allow a character to disappear behind a background element or to cut a virtual hole into the layer itself. The Mask requires a matte input.
Use the Mask editor to invert the effect of the matte on an image. Instead of the object being hidden by the mask, it will only be visible where it intersects with the matte shape area.