Complete means that something is finished, or has all of its necessary parts. When the mechanic hands you your keys, you hope that the work on your car is complete, and he hasn't left out a few important pieces of your engine.
Complete can be used as an adjective to describe something that is whole or finished, like a complete turkey dinner, which includes not only the bird, but also the stuffing, potatoes, cranberry sauce, and gravy. Another way to use complete is as a verb meaning to make something whole. Adding candles completes the birthday cake.