If you have a guitar amp with Send and Return jacks you could run a cable from the -10dB Main Out on the mixer to the Return jack on the guitar amp. Plug your guitar into a Hi-Z input jack on the mixer and slowly bring up the Volume on that channel. Set the Master maybe about 12 o'clock for starters. The Hi-Z input may have enough gain for a guitar (maybe). If you have a guitar amp that doesn't have Send/Return jacks, then try the main guitar amp input with a volume set really low to begin with. Try each channel the same way.
You could play a bit with the reverb controls, but I think the reverb may an external unit. If you give the mixer a bit of a light whack and you hear a springy boing noise from the amp, it's got a spring reverb inside it.