Keep only the overlap
Keeps only the piece two shapes share, which is how artwork gets trimmed down to a window, a badge or a rounded end.
1
Select both shapes. Neither one is the cutter here, so the order does not matter.
2
Only the piece where they cover each other is kept.
3
Everything outside the shared piece has gone.
Every setting
1What each number in the dialog means, and where it starts.
Keep originals
Keeps the shapes you started with, and adds the result beside.
What it is
Keeps only the piece where the selected shapes cover each other, and drops the rest.