Even though then and than sound similar, they really are two different words.

Than is used only in comparisons.
   The sun is far brighter than the moon.
   At least four buildings are taller than the Empire State Building.
   Sometimes a photo can explain better than words.

Then is not used for comparisions but usually has a time element to it.
   I will go to the restaurant then eat a great meal.
   They wanted to leave early in the moring but I wasn’t ready then.
   If you want to go to college, then you need to study in high school.