At any time hit the mixer button at the top right and you’ll see the stem sliders appear where you can set up your instrument mix.
There are 14 instrument stems in every song. Lead vocals, background vocals, acoustic guitar, 2 electric guitars, 2 keyboards which is often but not always a piano on keys 1 and something more textural like a pad or Hammond organ on keys 2, bass guitar, drums and a range of click tracks and vocal cues. In some songs some stems may be silent (i.e. have no backing vocals).
You can mute any instrument stem by clicking on its stem name. It will turn red when muted. Hit it again to unmute it.
Pressing the S button directly underneath the stem name will solo that stem.
You can also boost or cut the level of any instrument stem with its respective slider.
Finally on the very left there’s a pale grey master slider for overall volume control.
Settings are automatically saved per song, so even if you go to another song and come back those mix setting will be ready to go when you’re ready to play.