So the first chord you need to learn is how to play a major chord. And the basic formula for a major chord is the root note, then the not two steps away, then the note one step and a half away. So the C major chord would be C, then two steps is E, then a step and a half is G. So C, E, G is the C major chord.

Now the formula for playing the C minor chord is to take the second note which is E and lowering it one half step so you have Eb. So the C minor chord is C, Eb, and G.

From there you can form the Diminished chord, and what you do is lower the third note one half step. So the C diminished chord is C, Eb, Gb. And you can apply that to any note on the piano for finding the Major, Minor, and diminished chords.

Now the last basic chord you can form is the Augmented chords. And what you do is take a major chord, and raise the third note one half step. So a C augmented chord is C, E, and Ab.

These are the four basic chords you can play on the piano. From there you can add things like major 9th and 11th and 13th. But you can find a piano chord chart that will give you all the chords but it is good for you to know how the chords are formed and why they are formed.

So to play the 9th chord the 11th and 13, you basically just instead of looking at the scale as letters you count it as numbers. So if you are playing a C major chord, and you want to add a 9 to that chord which will give it a fuller sound You just count up nine from C. So you end up with D and from there you can find the 11th just keep counting and you get to F. Then from there you keep going up to the number 13 and you have your 13th note.

So basically the 9 is the second and the 11th is the fourth, and the 13th is the sixth. They are the same notes you just don't ever call it a C 6th chord it will be a C 13th chord. So the 13th is where you not only add the 13th but you add the 11th, 9th and seventh. You add these notes only to put a fuller sound to the chord so a C major 13th chord will be C in your left hand and Bb in the left which is the seventh note. Then in your right hand you have C, F, and A and you discount the E and G.