Farseer is based on Box2D which has a pretty good manual. I would not say great manual but which open source engine has a great manual?
Also these two sites are full of tutorials for Box2D (first one is C++, second is Flash). The concepts are the same.
The old manual for Farseer 2.x (before it was converted to be a port of Box2D) could be useful too although many things have changed.
The TestBed is full of great examples.
I also regularly peruse the sites/forums of other physics engines like Bullet, Chipmunk, ODE, Newton, PhysX, Jitter, BEPU. Each can help since Newton's laws are valid everywhere if you are an inertial observer :)
Finally stackoverflow.com and its sub-sites http://physics.stackexchange.com/ http://gamedev.stackexchange.com/ have quite a few answers.
At the end of the day there is huge amount of useful documentation if you are willing to mix and match and also read the source. It's more problematic to describe your problem in physical terms...
As I beginner I started modifying the TestBed which quickly proved very productive before moving to my own models. I'd recommend going from there.