Pianomarvel is an app you can get by going to pianomarvel.com. They have an amazing number of ways you can use it.  The best I think is on an Ipad, but you can use your computer as well. If your piano or keyboard has a midi connection or a usb connection you can connect it to the computer or Ipad and use the app.  If you are just learning you can use the lessons to start from the beginning or maybe further along. If you are already able to read music, they have an enormous library of music you can learn. It is very helpful because you can take out certain parts to work on, or just one hand at a time, or slow it down.  The app gives immediate feedback about what you played on time, what was wrong and what was right. Since practicing correctly is the most important part of practicing, that is very valuable. And it is impartial. No arguing. 

I won't lie. If you put in my name (Dunning) as the Distributor, I do get a couple of bucks a month. They charge $19/month and there is a free trial. Get this app and try it!