How does the harmony change the melody?

Answer:
By the chords that it uses. Mainly, the melody is written, and then the harmony is put underneath it using chords that have the right note in them. For example, if a melody went D, A, B then in the key of C, the chords could be: DFA, ACE, GBD. Does this help?
First answer by Marma-duke. Last edit by Marma-duke. Contributor trust: 4 [recommend contributor recommended]. Question popularity: 2 [recommend question].