Clipping paths allow you to cut out one shape with another. This is sometimes called masking. To use one of your shapes as a clipping path for another shape, first select the shape you want to clip. In the Inspector, press the Clipping button and select the path you want to use as a clipping path, or mask. Flare can use any shape as a clipping path, regardless of where it is in the hierarchy.
Note that you can use multiple clipping paths: