The Gang of Four is original. The follower's books are easier to understand. For instance, you can also try to read Mark Grand's two-volume book. In addition, if you visit www.gamelan.com, you can find some very good tutorials about patterns. I don't think one can master so many patterns within a short time. But if you know marker pattern, immutable pattern, singleton pattern,
factory pattern, facade pattern, observer pattern, ..., model-view-controller patter,
it will help you a lot. In my programmer carrer, I have ever been asked by interviewer about factory patter and singleton pattern.