I know I am a little late, but I wanted to add a little something to the original post about major third and minor third intervals, just in case it may help someone else( I also teach piano lessons and my eleven year old student had some trouble with this very concept.)
A major third has a measurement just like a minor third has a measurement.
On a keyboard, we don't measure inches and feet, we measure half steps and whole steps.
Therefore, a major third is 4 half steps from the start note, and a minor third is 3 half steps from the start note.
For example, on the C major chord, we had C-E-G.
C-E is a major third. If your finger is ON the C, then you start counting on the C#(1) D(2) Eb(3) E(4) that equals 4 half steps.
It is important that you start counting on the very next note from the one you start on, otherwise you will be one off. The simple principle applies to the minor third E-G. Your finger is on the E, so you start counting on F(1) F#(2) G(3). and the interval for the C-G called a perfect fifth, is seven half steps, which makes sense because 4+3 equals 7. Now the important thing here is to do as TBlock said. Memorize your basic triads. They are your foundation chords. Learn the formula, but do not try to get by trying to count out half steps when you are playing chords. It is too slow. I only posted this to help you figure out the chords to memorize.
Use the formulas TBlock laid out for all of the chord types and then memorize them. You will be well on your way!! I hope this helps somebody!!