Connect the GT-8 to your computer using the digital audio cable to the computer digital input. Connecting digitally avoids extra digital-to-analogue conversions. Alternately an amplifier output can be connected from the GT-8 to the light blue jack on a standard sound card, using the 1/4-inch to 1/8-inch adapter.
Connect any sound source with a 1/4-inch phone jack to the input of the GT-8 directly. If you are using a device such as a microphone with an XLR connector, you will need an audio mixer to convert the signal for use with the GT-8. Take care with signal level out of the mixer as it may distort the input stage of the GT-8.
Adjust the parameters of the GT-8's effects and simulators to shape the sound source you are working with. The GT-8 will allow you to try effects normally used with guitar on other sources, such as wah-wah on vocals or distortion on keyboards.