Use the [Z] key to jump, the [X] key to jump/go back, the arrow keys to navigate/move, and the [ENTER] key to select.
FYI.. The game doesn't save your data. You have to download your play state.
I play this title all the time at school to fill time. I have all 5 save slots fully complete, but that doesn't stop me from speedrunning levels! If you know me irl (somehow), this is what you're seeing me on pretty much half of the day. LOL