I learned the basics of C outside of FIRST, which I think is much easier to understand rather than jumping into the robot right away. I was just in the same position as you (except for an offseason competition) and these are my tips to anyone just starting to program for FIRST.
http://aelinik.free.fr/c/ is the tutorial I used.
You could only do the first 10 lessons and have a basic understanding, but like everything else, the more you know, the better off you'll be. Learn as much as you can
before the season starts.
During the season, remember that your main goal (assuming the game is similar to prior years) is to have the controls running so that the controls are natural to the driver. In order to do this efficiently, make sure that you understand the electrical system, as it is the core of everything you program for. Watch everything that the electrical team wires and ask as much as you can about what they are doing.
Once you have the controls "done", you should at least attempt an autonomous (again assuming that it is in this years game.) Whether you attempt to score or just set the driver up for an extra few seconds it is very effective in helping your team. Just remember to start small with your autonomous and add to it little by little until you understand everything and have a finished product.
For the specifics on how to upload code to the robot the best place would be the programming section posted above.
Remember don't be afraid to ask about anything on here, everyone here was a new member once and knows how hard it is to jump into something you have never done. Just keep working at it and you will improve.