Last few days I'm trying to start with farseer library, however i just can't get anything work properly. Documentation is very poor and there aren't many ( any? ) resources on the internet relating to 3.3.1 version. It's my first time trying to use physics engine, so it is even bigger problem to me.
There are examples in their tutorial section as well as their sample source code. In particular, if you want to see how a certain function can be used, you should go through their Test Bed source code which demonstrates how to the use main functions in XNA.
For theory, and possibly other methods, you can look for documentations related to Box2D. Farseer is a port of the Box2D engine, so most information from Box2D can be transferred to Farseer quite easily.