Then is used to show that something happened in the past, IE: "He then punched his face off"
Or talking about order, as Messes said.
Than is used to make comparisons in some cases, IE: "Greater than"
Them is a pronoun used to refer to a group of people, of which you are not a part of, IE: "Take it from them"
Their (I assume you mean "their") is a possessive pronoun used to show that another group possesses something IE: "Their crap"
Your is a possessive pronoun, used to show that one person owns something, IE: "Your crap"
You're is the conjunction of "You are" and generally used in the same context, IE: "You're stupid"
Some of this info might be wrong.