Locate middle C on the piano. It will be the white key directly to the left of the two black keys nearest the center of the instrument.
Play middle C with your right thumb. This will be the first note, or "root" of your chord.
Count each key (white and black) beginning with the black key directly to the right of middle C until you reach four piano keys above middle C. (What you're counting are called half steps.)
Play the piano key that is four half steps above middle C with your third finger on your right hand. This is E.
Play C and E together using your thumb and middle finger.
Count three more half steps to the right of E, and play the note with your right little finger. This note is G.
Play C, E, and G together. This is called a C chord.
Repeat this process beginning with various keys on the piano.
Recognize the names of notes as you do this. The progression of white piano keys are C, D, E, F, G, A, B, C. Black piano keys are "sharps" or "flats" of the white keys. Sharps are to the right of a white key, and flats are to the left. For instance, the black key to the right of middle C can be called C sharp or D flat, depending on which chord progression you're playing.
Play major chords by using the formula of the root, plus four half steps and then three half steps.
Play minor chords by using this formula: the root, plus three half steps and then four half steps. (To put it simply, major chords have a happy sound, and minor chords have a sad sound.)