Go to the C below middle C on your piano, and place your little finger on the C, your middle finger on the E and your thumb on the G. This is a C major chord, formed with a major interval--C to E takes four half steps--and a minor interval, from the E to the G, or three half steps.
Play the middle C with the thumb of your right hand, while sounding the C major chord with your left. By striking middle C 3 times, then a D, then an E, you are playing the first few notes of "Row, Row, Row Your Boat," with the accompanying chord.
Form a minor chord with your left hand by playing C, E flat and G. The two intervals that form the chord are a minor interval on the bottom--the C to E flat--and a major interval--E flat to G--on top. Notice that the sound of the chord becomes more sad, almost forbidding-sounding, a characteristic of minor chords. Play the middle C with your right hand and hear how the mood has changed.
Play the C major chord again with your left hand again, but this time use your index finger to play the G and put your thumb above it on the B. This can take some stretching, but even if you have to roll the chord by playing the bottom part first and then sounding the B, you should still get the feeling that the C major chord has gone from sounding happy and basic to having a quality that is more uplifting, even spiritual. Your C chord is now a C major seventh chord, a mainstay of contemporary music. In fact, if you play a quick E with your right hand and then a G, while voicing the C major seventh with your left hand, you've just played the beginning of "The Impossible Dream" from the Broadway play "Man of La Mancha," as well as the beginning of "A House is Not a Home," performed by Luther Vandross, as well as countless other songs.
Play the C major chord with your left hand, and this time put your finger on the B flat. You will notice there is a sound of expectation, of something waiting to resolve. You've just played a dominant seventh chord, an indispensable chord for playing blues. The dominant seventh chord is also used in songs to bring the music back to the beginning chords again.
Put your left hand on the G below middle C, and form a G major chord by playing G, B and D, a G minor chord by playing G, B flat and D, a major seventh chord by playing G, B, D, and F sharp, and a G dominant seventh chord by playing G, B, D and F. You have just changed the key, or transposed, by voicing the C chords you learned in the key of G.
Play the beginning of "Row, Row, Row Your Boat " as you did in Step 2. Continue on with the melody, sounding it out if you have to.
Play the G dominant seventh chord with your left hand when you get to the part of the melody where the word "life" occurs.
Walk the melody down from G to C--the lyrics would be "is just a," and when you reach "dream," switch to your C major. You have just played a song and accompanied yourself with left-hand chording.
Transpose the chords you learned to all 12 keys, proceeding like this: C, G, D, A, E, B, F sharp--also called G flat--C sharp--also called D flat, G sharp--also called A flat, D sharp--almost always called E flat, A sharp--almost always called B flat, and F. It seems like a tall order, but once you have these chords under your fingers, you will be able to accompany yourself in any key.