I am not familiar with free online piano lessons. I would suggest going to your local music store and asking if they can recommend a teacher. The benefit of having a teacher is that they can tell you what you are doing right and wrong. The best way to learn is from a hands on teacher.

If you don’t want to pay for weekly lessons, there are adult piano method books available. I would suggest the books if you have some music background. If you don’t know much about reading music, you might not know if what you are playing is correct.