Chords are a very important part of our musical language. Composers use chords to harmonize melodies and establish the key of a piece.
Here you can see how Beethoven's Ode to Joy melody can be harmonized in a very simple way. Some chords are in inversion (what is an inversion?). See the links below for more information about inversion and other related topics.
See our reference for more information about chords:
We also have seventh and extended chords exercises in our exercises section.