Try searching Google for "serial port programming C." Truth be told, I don't do a lot of C programming so I can't really help you there.
What I can tell you, and if you want to start programming using the serial port right away, is to download a free copy of JustBASIC. All the serial port programming capabilities of a C program with none of the hassle.
We don't mind helping you but we won't do all of the work for you. Please post what you've already done including any ideas you've had and we might be able to make some suggestions. If you've got completely no idea then may be it's your lecuturer's fault and it isn't right that you make him/her look good by cheating and copying from the Internet.