I almost got a Math degree but want to learn better topics in group theory, expecially about finite ones. I studied just introductions on groups (in the firsts algebra courses) and something about group actions and theory of characters. Could anyone recommend a good book on the topic? Thank you
For the representation theory of finite groups, I suggest Serre's Linear Representations of Finite Groups.
Contemporary Abstract Algebra by Joseph A Gallian
As already mentioned, Gallian's Contemporary Abstract Algebra is a good place to start. I also really like Dummit and Foote's Abstract Algebra, though this is primarily a first year graduate text, so it may be a bit terse in some places.