There are numerous “teach yourself to play piano” packages out there for sale. If you had music class in grade school and can carry a tune at all you should be able to teach yourself with this article and it will cost nothing but your time.
Firstly you do need to know the notes of the piano keyboard, C D E F G A B C with the black keys being the sharps and flats. Black notes higher(one half step) than a standard note is a sharp, those one half step lower is a flat. You will also need to know the singing scale from your grade school music. Do, Re, Mi, Fa, So, La, Ti, Do, these going from low Do to high Do making one octave. Armed with this knowledge you can learn to play. The first Do is #1 or a 1st, Re is a 2nd, Mi a 3rd and so on back to the high Do which is an 8th. Since you know the notes of the piano and the Do, Re, Mi scale you can pick any note and make that your low Do then find the Re and so on, you can jot this down in a notebook which would be a good piece of equipment to have if undertaking this task. The key of C ( from C to C listed above) is the easiest to explain since there are no sharps or flats in this key. C is Do or a 1st, E is Mi or a 3rd, G is So or a 5th, remember a 1st, 3rd and a 5th is always a 3 note chord. In this case the C, E and G will be a 3 note C chord called a triad. No matter what note you put as your first Do this rule always stands true. Do is always a 1st. To make a minor of any triad you drop your 3rd one half step. In the case of the C chord you would drop your E note to the black key just below it to make a C minor.
Now that you have that knowledge it wouldn’t hurt to get to the basics of a rythm and blues progression. Go back to the Do(1) Re(2) Mi(3) Fa(4) So(5) La(6) Ti(7) Do(8). A three chorded R&B progression is the basis of both the 8 and 12 bar blues, the seed that grew to most modern music. It is a 1st, 4th and a 5th. This is the pattern of more classic songs than I can begin to count.
Let’s build a 7th, this makes the music sound a bit more bluesy. Many times a minor 7th is the real deal. To build a 7th, count up 6 notes starting with the 1st (Do). When you get there add the note one half step above that and you will have a 7th. Ex. a C7 would be a C, E, G & Bb. Even a little funkier is the 9th. A quick way to build a 9th is to drop the root note and put the 7th on the bottom. The traditional method is to drop the root note and add the 9th or 2nd Re. Start with an inside out C7 which would be from low to high G, Bb, C & E. To make the 9th drop the root note and add the 2nd Re. The traditional C9 would be G, Bb, D, E. You can compare it to the short version which would be Bb, E, & G and use whichever sounds best for what you’re doing.
This learning is easy to transfer to other instruments. The bass player for “Yesterday’s Hooligans” was my first student and is now in one of my part time bands.