Does someone know a good book or site or something about opamp's
One of best book I've seen was by Jiri Dostal (1993). It is very rigorous and is not for the casual reader. But it has very clear explanations. The book is very expensive though (see amazon). Its best that you borrow a copy from your school's library before you invest.
Walt Jung (2004) is also good for applications. You can also use Horowitz and Hill (1989) which has some good material on op-amps.
Before Internet, National datasheets books were nice, with lots of examples and explanations.
The Art of Electronics by Horowitz and Hill has a good introductory (and very practical) treatment of opamps:
Beyond that, wikipedia.org has a good intro page, with lots of links out to other info:
I like Design with Operational Amplifiers and Analog Integrated Circuits by Sergio Franco
Separate names with a comma.