When playing piano, you need to play piano with slightly curled fingers so that all fingers can rest on the keys.
Turn your hands upside down so that your fingers naturally curl upwards. Now flip them over and put them on the keys. You’ll be playing by pressing down on the tips of your fingers. You’re thumbs should be resting on the keys as well.
Your arms here should be straight and one thing you’ll really need to be conscious of with no teacher there to correct you is not to rest your wrists on the edge of the piano. It’s a bad habit that you’ll want to avoid.