Audacity should do the trick or tuxguitar.
Do you have a dedicated sound card?
To manage latency and routing you should use jack2 the gnu/Linux audio server.
If your amp have an output ou should plug : guitar to multi effect to amp to PC in. If your amp doesn't have an output, you shouldn't probably use it and go : guitar to multi effect to PC in. All this should be in mono, except if your multi effect's output is stereo.
Yes it's a guitar tab soft, maybe it can't play from an input. With jack you can plug the sound card input to the output to ear the guitar sound.