To accentuate something is to emphasize it. If you use a lot of emphasis to describe part of a meal, as in "the steak was SOOO good, and I liked the salad too," you "accent" what "-u" "-ate," or accentuate, the highlight of the meal — the steak.
There is an old song with the lyrics "Accentuate the positive, eliminate the negative." The drawn-out pronunciation of the word accentuate (ack-SEN-chew-ate) draws attention to the word, which is exactly what accentuate does: it draws attention to something. Sometimes, though, a negative quality gets the focus, as in "his bad mood did a lot to accentuate his reputation as a grump," but the negative is usually an unintentional way to get attention.