I have a gateway ZX4931 computer with a built in webcam but I can not figure out how to use it.

Is this a laptop or in a monitor connected to the tower of a desktop?
the webcams usually are located in the Control Panel of the Start button box. in control panel look for hardware devices, cameras, etc and click on that choice. it should list your webcam. it may be in the Programs list of the Start button(All Programs). It will be listed by the model number or manufacturer name. click on it to run the program if it is found. read the instructions or 'read me' file if listed under your webcam listing