Commands

D F J K or 1 2 3 4: the four lanes. Hold the key for hold notes.
Touch: while playing, the screen is split into four tall lanes; tap or hold anywhere in a lane. Multi-touch works for double notes. The 1-4 buttons and pad work as lanes too.
Song select: arrows pick a song (Up/Down jumps a set). 3 changes the chart (Easy/Normal/Hard), 2 toggles Practice, and OK or 1 (or a second tap) plays.
Menu: 1 Songs, 2 Endless Mix (Daily Song in Daily mode), 3 Skins, 4 Calibrate, 5 Log off (press twice).
Calibrate: tap a lane key on each beep. Left/Right nudge the offset; OK or Back saves.
Backspace / B: press twice during a song to quit. On the other screens it goes back.
P / Esc: pause.
Choices menu: pause, how to play, new game, sound, difficulty, save slot, theme.