Based on many studies, it takes 10000 hours to become a grandmaster at any instrument.
Since the piano is one of the most complex instruments, as the player can perform either chords, harmonies, melodies, rhythm, many voices (and all of these at the same time!) it is not only enough to be able to perform a song,
sooner or later it comes necessary to understand music theory, as well.
However, not everybody wants to play as a professional, some students want to just play something for their loved ones, some students want to play easy songs, some students want to know more about music, and some just want to have fun with the piano after a long day!
Under the different menus, you may see what kind of lessons you should take.