Have you looked at Patrik Hägne's sample/tutorial? It's a little old, but may help.
As you noticed, the documentation could use some fleshing out. We're working on it.
An alternative would be the PluralSight FakeItEasy course. I've watched it and thought it to be quite good. I think it's short enough to watch as part of their free trial.
Me, I was familiar with mocking concepts and just tried it out. The fluent syntax guided me along well enough. Try it - you may be pleasantly surprised.