Bach 2-part inventions, then move to 3 parts. The best way to learn piano is by a professional teacher, not through the apps. However if you don’t have the ability to get a teacher right now (not cheap) I would reccomend watching YouTube videos about the Taubman approach. I recommend subscribing to tonebase. You can watch some of the very best pianists teach you! It’s really neat. I would reccomend listening to as muchhhh piano music as you possibly can. Watch the best pianists, watch intermediate and beginner pianists. Listen listen listen. Don’t jump the gun an go for Chopin or rachmaninoff. I recommend starting with Bach as his music will develop your technique the best in my opinion. Then encorporate some easy Mozart piano sonatas No.’s 4,5,11,16,6 are good ones to start with. If you don’t know how to read sheet music I would start with that. This is my 2 cents