photo help

so I have been married a year and still are yet to have an album in my hands. My one regret would be using a 'friend' for my photographer. He missed some key photos and now I cant turn back. I dont know much about Photoshop and I thought that he did. Anyway, can someone fill me in on the types of things you can do with in. Can you lighted pics that are too dark? Is there anyway to create pics that werent actaully taken by combining other pics?
Any help would be GREAT!!!! Does anyone know someone that could maybe help me?