How do I layer mask

How do I make a layer mask so for example I have a square tiled background, and i make a round circle object on top of it, so the tiled background will be a circle, ie a kind of layer mask?

so only the shape I make will show through of the tiled background.

have you checked the blendmodes example from the new project dialog?

nevermind i figured it out. have tile on bottom and set destination over, and have the shape you want to show on top and say destination out. all on same layer