A complete sentence is a sentence you can say to someone, and the person will understand it. Use correct punctuation. Punctuation doesn't have to be complicated. Use common sense as a guide. Sentences end with a period.
Questions end with a question mark.
Use exclamation points for exclamations and commands. Commas tell readers when to pause. They separate items in a list, or clauses in a sentence. If you are having trouble with punctuation, your sentence structure may be too complex. Start over and phrase what you want to say more simply.