synth shield audio in

I went ahead and added a guitar plug into the audio input on my solder your own arduino kit with synth shield I can hear the crackle of the guitar being plugged in, but I don’t hear any other sound from it, other than the existing synth sounds the kit had me program in. Do I need to adapt the code in order to amplify the signal to the speaker or something similar? Has anyone done this with their synth shield who’s could help? Many thanks!