We use “than” when we are comparing and contrasting.
e.g. Maria is better at English than Juan.
e.g. Studying is more important than going to the party!
“Then” has many uses.
1. When talking about a certain point in time.
e.g. I was happiest when I lived in Spain. I was really happy then.
e.g. I can’t wait to see you for lunch. I’ll call you then!
2. We also use “then” to express “next” or “after”
e.g. I am going to study English and then go to the gym.
e.g. Eat your dinner and then we can have ice-cream.
3. We also use “this” to express “also”, “as well as” and “additionally”
e.g. He drank a milkshake and then a fruit smoothie
e.g. It’s £5 for the parking, then another £10 for the tickets!