I'm not sure if this is what you're looking for, but....
Let's assume you want to cut a dog shape out of the background. You have 2 layers - the background layer and the layer with the dog. Use the selection brush to select the dog, refine as necessary, and then untick the dog layer (making it invisible) and select the background layer - the selection will be applied to that layer and you can delete it or change it as you wish. You can use the Move tool to reposition and or resize the selection if you need to.
