activating a serial port in c

I'm trying to access a microcontroller connected to a PC via a serial port.. I want to get the serial port opened and send a command to run a programme to activate a relay attached to the microcontroller. I want someone to help me with the c/c++ codes.

I'm very new to programming and i know very little of c/c++. I'm learning now. but I need this to be done asap. So please can any one help me with this...???

thank you very much