The words then and than look similar, but their uses are very different.

Then

The word then usually relates to time. It is most commonly used as an adverb. It has the following meanings:

Subsequently or afterwards

• Go to the traffic lights, then turn right.

• It went dark, then there was a scream.

• The council members argued for three days then eventually came to a decision.

As a consequence or in that case.

• If you had cleaned your teeth properly, then you wouldn't be in this predicament.

• You're certain then?

• If that's how you feel, let it go then.

At that time or that time.

• I was much fitter back then.

• She used to holiday in Sri Lanka as it was then known.

• The schedule will be completed before then.

• It was the responsibility of the then team captain to account for the trophies in the cabinet. 
(In this example,

then

is an

adjective

.)

Than

The word than introduces a comparison. It is most often seen with comparatives and words like more, less and fewer.

• Craig is smarter than Paul.
(

Smarter

is a comparative.)

• Money is better than poverty, if only for financial reasons. (Woody Allen)
(

Better

is a comparative.)

• Russia is even more spacious than Canada.
(

More spacious

is a comparative.)

• I have less space than you, but I also have fewer workers than you.