Hello jleisek,
Thanks for using Apple Support Communities! It looks like you need some help with GarageBand, and we'll be happy to do what we can to help.
If you're using macOS Mojave, take a look at this article: If you can't record audio after installing macOS Mojave or later
Otherwise, see if these two articles can help:
GarageBand for Mac: Use the bass amp controls
GarageBand for Mac: Use the bass amp effects
From the GarageBand Help guide: Before recording audio
If you need additional assistance, we'd suggest contacting Apple Support for GarageBand.
Get Support > Select Music, Apps & Services > Mac apps > GarageBand
Take care!