I agree with Thorham.
If you want to learn something that you can use everywhere, stick with C. If you choose to make your objective to learn C, then I'd suggest to put amiga specific programming in the background and focus on the language itself. Find (google) the "the c programming language by kernighan and ritchie". Go through it. Write the included programs on your amiga. Compile them. Run. Make yourself familiar.
Writting a 'wc' (word count) program feels good for a newbie!
At least it did for me!
Whatever you do, just have fun!