Confusing then and than is a mistake we frequently see online, even made by native speakers. Although their spelling and pronunciation may appear similar, they have very different meanings.
Than can be either a conjunction or a preposition.
It can be used to join two parts of a comparison or used with 'more' or 'less' to compare numbers or amounts:
I am a lot older than my brother.
There are fewer people here than last year.
I would rather go to a restaurant than a bar.
It’s colder than I expected.
Then has more than one meaning but it is generally used when talking about time and the order of events.
When used to refer to a particular past or future event:
When I lived in Los Angeles I surfed every day.
She's going to the party too, so you will see her then.
Call me after 7pm, I should be back by then.
When used to show the order of events or actions:
First I have to pick up James, then Peter.
Finish what you need to do, then we will go.
Now decide if these sentences need than or then: