You need an audio interface to your computer, a sound card or something like it. There are a bewildering variety of them available today. You need to decide what you want to do and that will dictate what type of device or devices you need. Obviously, for a start you want to record your guitar playing direct from the G-Force. You would want a sound card with the matching type of digital I/O, which I suspect is S/PDIF -- might as well use those digital outputs if you got them. Some sound cards are strictly audio interfaces, e.g. the M Audio Delta 66. Some also have MIDI interfaces, e.g. the M Audio Delta 1010... some even have MIDI synthesizers, though these are usually the cheaper consumer-type cards or more expensive ones like the Creamware Pulsar. The there's analog inputs --some have 2 ins and 2 outs, some 2 ins and 8 outs, some 4 ins and 4 outs, or 6, or 8... Some even have decent microphone preamps so you can plug a mic right in and not have to get a mixer or outboard preamp...
Reading a lot throughout this website is a great start on locating potential candidate devices...