Have you seen the first two videos? If not you can check them out here: Video 1 of 3 and Video 2 of 3. In Video 1 you learn the names of the keys, and Video 2 you learn 5 note scales.
Now you are being introduced to chords. Chords are formed when you play 3 keys at the same time. They are generally built with the 1st, the 3rd, and the 5th note of the 5 note scales you just learned. Again, if you are a brand new pianist and this is your first lesson, this will make sense, over time. The most important thing you can do is play. Play with the cards all over the piano, on every key, with either hand, backwards and forwards. Over and over again. If you say the names of the keys as you are playing them (see Video 1) even better!
These 3 videos make up a 30 minute lesson. With the Key Name Card and a set of the 5 Note Scale and Chord Card, my students have enough to start laying a really strong foundation for playing the piano and sounding musical from the beginning.
The cards make it possible to play accurately from the beginning, so every time you (or your student) plays, progress is made and learning happens.