Here's a link to some programming tutorials my wife (and fellow mentor) created to teach our students the basics of programming in C. She taught AP Computer Science for several years and used that experience write tutorials to get new programmers started.
http://idleloop.com/tutorials/introC/index.php
There's still some more work to be done, but we've had good success using these materials to train a new crop of programmers this year.
The tutorials intentionally avoid using C++ features that are not available when programming the robot, and everything is very platform agnostic for the same reason.
You learn to program by doing, not by reading, so read the materials, work the exercises and try the "further explorations." Once you get through the tutorials, you'll know enough about C that you can learn the specifics of programming the FIRST controller.
The kit of parts comes with sample code to get started and there other good sources of sample and library code on Chief Delphi. All of that will make a lot more sense once you have the basics of C down.
I'm always happy to answer questions about either the tutorials or programming the FIRST controller.