The fpc documentation is extremely good.
Err, then why do I see so many bug reports in the bug tracker filed in the category “documentation”? I mean, they're solved, but every month new ones are reported.
Also – I can't tell you how many times I've combed through the sources – but we got lots of stuff already prepared in the RTL, FCL and otherwise packaged. If you have to glean documentation though, just to get things started, this is no fun.