To be honest, Rockbox is kind of hard for people who don't do much coding.
I know many programming languages, and I started writing a Plugin for Rockbox a few weeks ago.
The lack (ahhemm) of documentation (the most useful doc is existing code, basically) and all the low level C stuff is already making me going nuts day after day.
Well, all that said, welcome to the community. The language you must learn is C, not C++. There are a lot of difference between them and a lot of similarities too.
I would suggest picking up a "C for Beginners" kind of book from your local bookstore first.
Best of luck.