Could someone give me some information on genies?

A character in this book I am writing is a genie. I don't know much about genies. Some texts say they have free will while others say that they are bound to bottles or lamps and must serve whoever releases them. So my questions are: Do all genies come in bottles or lamps and how to they get in there? Are they immortal? What do they look like? Also, could you provide websites or books that have good information on genies? Thanks.