If you are comparing two things, use THAN.
- Anna is taller THAN Ben.
- The big house costs more THAN the little house.
- Clothes from the Gap cost more THAN clothes from Goodwill.
THEN deals with time, or it shows a sequence.
- I want you to take a bath and THEN go to bed.
- First you must eat your peas. THEN you can have dessert.
- Take a left on First Street, and THEN a right on Pine Avenue.
Until next time, Grammarians…