Usually, the fastest way to learn how to play the piano is with a teacher. They not only know the scales, songs, and chords that you need to practice, but they can give you specific advice on how to improve your playing. Make sure you like the teacher to a fixed term. When looking for a teacher, be sure to discuss the following:  Your goals in playing the piano (songs, bands, career, etc.) What genres of music you want to practice The teacher’s qualifications and experience The teacher’s cost and availability Most piano music is written on charts in musical notation, and it is rare to find a piano player who cannot read music. Purchase a book, watch videos online, get a music learning app or ask your teacher to help you learn so that you can play any music you can get your hands on. Practice reading music each day so that it becomes second nature. You can try to play pieces by sight, bring charts with you on the bus, play songs frequently or play musical games online. Music is built on a set of rules and relationships between notes, and knowing music theory allows you to see the patterns in your favorite songs and learn them more quickly. You can always take a course, but there are also a variety of books and online tutorials meant to teach people music theory, from the basics to complex arrangements. Available at every music store, these books are relatively cheap glossaries of every piano chord you could play. They are usually grouped together by note, but frequently they come with sections detailing which chords sound good together and the right scale to play for each note.

Summary:
Hire a teacher for personalized, hands-on lessons. Learn to read music. Learn the basics of music theory. Buy a chord and scale book.