Locate the "line in" input on your computer's sound card. This is usually located on the back of the computer; however, many computers are now equipped with these inputs on the front of the computer for ease of access.
Plug the 1/4- to 1/8-inch adapter onto one end of the guitar cable.
Plug the 1/8-inch jack into the line in of the computer.
Plug the other end of the cable into the electric guitar.
Open your sound management program on the computer and mute all channels, except for the line in. You can reach this the sound management program by going through the control panel and clicking "Sounds and Audio Devices." Adjust the volume accordingly with both the computer and guitar controls.