Photoshop CS5 help please.

Its best to think of any image, even with one layer and no background still as an "open project".

If you open a jpg image, you will be able to add layers directly to it (and then save it as a ps file) and paste in what you want, or copy the area and paste it onto another open project.

also get used to using these A LOT:
ctrl a - selects everything on the layer
ctrl c - copys the section
ctrl v - pastes a copied selection

Okay so thats almost 99% not news to you, but they feature HEAVILY in creating multi layered images etc