Then is a word that puts things in order by time, or refers to a moment in time: you get up; then you have breakfast. You're married now; back then, you were single.
The word then can also be used as a consequence, often after the word if. If you watch the kids, then I will clean the house. Don't confuse then with than, which sounds similar. Than is used to compare two things: I like spaghetti better than macaroni and cheese. Then is about time or consequence: you eat dinner, then get dessert. If you're good, then maybe you'll get a big dessert.