Then: denotes a period of time or a sequence of events. "This is now and that was then." "First you do step A, then step B." Than: denotes a comparison. "He is taller than you are."
To that, may I throw in "explanate"? (explain, explanation..and for that matter, shouldn't the latter be "exPLAINation"?)
Along with my above criticism of "so", let me add "which". To me, it's very odd to hear, for instance"I went to the Red Sox home opener today, which I was glad to see the Red Sox won." Two solutions-1)-instead of "which", put a period, and make it two sentences, or 2)-"won" should be "win".