first of all, you do have a computer with an audio jack in, right?
i don't think you'll be able to plug your guitar straight into the audio jack. sure you can do it physically (you would use a 1/4"male plug to 1/8" male plug), but you wouldn't get much of a signal.
the problem with output from a guitar is that it is a very low signal, and needs amplification (which is why guitarists plug into amps). you may need some sort of amp with a line out, or maybe you can plug the guitar into a mixer, and then output the mixer to the computer.