In this lesson you have learnt two types of add9 chords which are formed by simply adding another scale tone to the existing chord. It is also possible to add other scale tones to chords.
You can add any note of the scale of the key you are playing in to any of the chords in that key. Each time you do this, it will change the name of the chord, but knowing all these names is not essential for now. The best thing to do is experiment and memorize the notes and chords which you think sound good together. The example below is in the key of E minor. It contains various scale tone additions and substitutions. Learn it and then use the ideas to make up your own progressions.