This Ableton Live clip covers three keyboard shortcuts that sit at the intersection of track organization and playback control. U folds and unfolds groups, S solos any highlighted track (and pressing it again disengages solo), and M toggles the computer MIDI keyboard on and off.
The M shortcut is the one worth understanding first, because when the computer MIDI keyboard is active, letter keys trigger notes instead of commands, which blocks shortcuts like U and S from working.