I just downloaded the trial version of the Tonelib gfx software but I don't know how to connect my guitar to the pc to use it. Any help would be greatly appreciated.
You need an audio interface, typically it would have a USB on one end and a guitar jack socket on the other, for example, one of the cheapest would be the Focusrite Scarlett solo. It's also possible that if you have a modern digital amplifier it would have an audio interface (for example Boss Katana has it, Line6 Catalyst as well). The cheapest option I know (and which I also use) is to buy Rocksmith Real Tone Cable, The used one on eBay should be less than 30$
Well, speaking of the cheapest... the PC sound cards still have a MIC In. It's 3.5mm, it's noisy, it does not have a knob, it's 16-bit ... but it's already there All you need for that is 1/4" to 3.5mm adapter, and your guitar signal will sound on the Microphone input in the PC OS. Some laptops these days have a combined jack (headphones and mic) like on smartphones, this will need a splitter cable in addition to the adapter above so that you could still hear the output. There are some cheap USB audio adapters, again Input for MIC and Output for Headphones. Technically it's an interface, just very much barebones. In many cases the sound quality is passable. Also USB interface could be plugged even in a smartphone via OTG adapter. For serious projects, a quality Audio interface is, of course, a reasonable investment. Though the PC itself should be powerful and stable enough for audio processing. Some multieffect pedals have an audio interface built-in. Also check out multitrack-recorders which also can have a built-in interface. Here's a video on "4 best ways to connect guitar to PC"