As a verb, to complement is to complete or to supplement. The wine complemented the meal.
As a noun, complement is something that completes something else. The addition of the B6 vitamin to my morning routine now gives me a full complement of B vitamins.
As a verb, to compliment is to praise. Don’t compliment me unless you mean it.
As a noun, compliment means praise. The compliment you gave me was insincere.