realistic shadows - help needed

[suladesign]

Does anyone know where to find ps tutorials concerning realistic shadows? I don't even know what they are called, but I'd like to start creating those type shadows where parts of the object seem to touch the paper, while others seem to be floating (useful for curled ribbons or photos/frames/papers where one corner/edge seems to come off the page a bit) - you know what I mean? Sorry for not being more clear on this. I guess, even to know what these type shadows are called would be useful, b/c then I'd know what to google ... lol