Than and Then

Than is a word used when making comparisons, such as when one writes, “I’d rather be in school than at work” or “Blood is thicker than water.”

Then indicates a sequence of events, as in this sentence: “Don cranked the wheel then shifted into third” or “If we hear the boat knocking against the rocks, then we’ll know that it has slipped its mooring.”

More Sentence-level Writing
Varsity Sentence Practice — Appositives
Quick tip about citing sources in MLA style
Who vs. Whom