Sean posted this link to an introductory graphics tutorial and info on graphics programming in C, in the C forum.
This is undoubtedly the best link I've seen, all year - do yourself a favor and check it out:
( Yes, I'm hyping it. No, I have no connection with it in any way. Yes, you'll be sorry if you don't check it out, if you're new at graphics in C, like me. )
On the left column, you'll see the other links to their tutorial. Good stuff there! (imo)