Piano instruction by a qualified piano teacher is the fastest way to get up to speed with the piano or keyboard.
If you have recently bought or inherited a piano and are thinking of learning to play then you should definately get piano instruction. Learning to play the piano on your own is very difficult as it is suprisingly hard to master. A piano teacher will be able to show you techniques and teach you skills and drills to greatly increase the rate you learn and the enjoyment you get from your piano.
If you live in a city then you almost certainly live near a piano instructor. Teaching the piano is a very popular pasttime. Putting in the hours to learn to play the piano is definately worth it. Playing the piano is a rewarding, therapeutic and relaxing skill to learn.