Listen and watch an American Goldfinch singing his song during mating season. You can tell it is mating season because he has his bright yellow and black plumage.
Some people use mnemonics and other descriptions to help remember and identify the sound of a bird. One of the mnemonics for the American Goldfinch is "po-tato-chip." Try as I may, I can't hear "po-tato-chip" in the American Goldfinch song.
You can read more about the American Goldfinch in the Backyard Birds section.