The official tutorials are the starting point if you want to learn how to use SFML. They explain step by step the important concepts and classes of each module.
Here is the reference documentation of the SFML API. It contains a detailed description of every class and every function of SFML. It is generated directly from the source code, with Doxygen.
SFML Game Developmenthttp://www.packtpub.com/sfml-game-development/book