Adding some flavor to major and minor
Start with a major chord or minor chord. Move the middle note from a 3rd to 4 or 2. Or do both. This creates sus chords. (Sus is short for “suspension”.)
You can also keep your major or minor chord and add 2. Technically an “add 2” chord has four notes, and so does the double suspension. But Xsus (Xsus4) and Xsus 2 are legitimate three-note chords.
In the time of Bach, a suspension chord was a means of creating tension and releasing it. There were no major and minor chords that added 2. Sus chords were never final chords. But today they are used anywhere, to add “color”. Today they can end a piece or phrase, and so can a major or minor chord adding 2. Impressionistic composers such as Debussy used sus chords much the same as contemporary pop and jazz composers.