I'd ban Nickona for not being able to use a dictionary.
"Then" is a measure of time, as in "back then, when I was younger".
"Than" is a measure of more or less, as in "His truck is bigger than mine".
then
1: at that time2 a: soon after that : next in order of time <walked to the door, then turned> b: following next after in order of position, narration, or enumeration : being next in a series <first came the clowns, then came the elephants> c: in addition : besides <then there is the interest to be paid>3 a (1): in that case <take it, then, if you want it so much> (2)—used after but to qualify or offset a preceding statement <she lost the race, but then she never really expected to win> b: according to that : as may be inferred <your mind is made up, then> c: as it appears : by way of summing up <the cause of the accident, then, is established> d: as a necessary consequence <if the angles are equal, then the complements are equal
than
1 a—used as a function word to indicate the second member or the member taken as the point of departure in a comparison expressive of inequality ; used with comparative adjectives and comparative adverbs <older than I am><easier said than done> b—used as a function word to indicate difference of kind, manner, or identity ; used especially with some adjectives and adverbs that express diversity <anywhere else than at home>2: rather than —usually used only after prefer, preferable, and preferably