Welcome to EH-Net and thanks for your service.
A good starting place are the pinned topics at the
top of this board. Also, check out the free sample chapters in our
book section. Since you know C and can read assembly, then 2 great books are
Hacking: The Art of Exploitation 2nd Edition and Shellcoder's Handbook (mentioned numerous times in the forums). Networking is also important, so look at something like
The TCP/IP Guide which is freely available online.
This should keep you busy for a while. Let us know if you have some specific questions. If you bring a little to the table, our members are eager to help.
All the best,
Don