"Dessert" and "sweets" can refer to some of the same foods, but the context is different - "dessert" generally refers to something served at the end of a meal - maybe fruit, but more often something like cake, pie or ice cream. "Sweets" can be any of these, as well as candy, eaten any time of day. ) There is certainly some overap in the use of the terms.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.