Something that's literally sugary is extremely sweet, like a sugary root beer float. If something is figuratively sugary, it's overly sentimental.
Candy corn, soft drinks, and jelly beans are all sugary — and so is the sappy Valentine's Day card your sister wrote to her crush. The adjective sugary comes from sugar, an English word that, unusually, traces its origin back to Sanskrit. Sugar comes from sharkara, "ground or candied sugar."