"Then" is used when you are describing the order in which things occurred. I woke up, then I took a shower. "Than" is used for comparisons. My sister is taller than I am. "Those' and "these" are plural pronouns. "These" is for objects or people that are close to you, while "those" is for objects or people that are further away. http://learnenglish.britishcouncil.org/en/english-grammar/pronouns/that-these-and-those http://esl.about.com/od/thebasics/a/this_that_these_those_determiners.htm

then = later than = compared those = several in the distance these = several here

"Those" plural for "that" for those far from us. "These" plural for "This". from those near us.

"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"

Watch out: many native-speakers in the USA will confuse "then" and "than" because of carelessness or ignorance. Same thing happens with "it's" and "its", plus "there', "they're", and "their".