WPILib Screensteps - https://wpilib.screenstepslive.com/s/4485/m/13809
This has a step-by-step guide on how to get your development environment setup and build some basic FRC programs.
WPILib Javadoc - http://first.wpi.edu/FRC/roborio/release/docs/java/
This is a list of all the classes provided by WPILib with documentation on what they do/how to use them, the methods available, etc
Great thread on Chief Delphi right now about drivetrain control - https://www.chiefdelphi.com/forums/showthread.php?t=152783
If you're just getting started in programming, here are a few links to resources that can help you get going: