Well, for starters, cF uses Photoshop. If you want to cut out parts of the picture, use the eraser or lasso tools, that way you can cut out only what you want.
With PSP layers are your best friend; start out with whatever you want as your background as the bottom layer, then paste the other pics you want to use as a seperate layer on top, erase out anything you don't want with the eraser or lasso tools. Try playing with layer blend modes, to do that go to Layers > Properties and experiment with blend modes and opacity. Be sure that you have it set to preview it so you can see what you're doing 🙂