Thenas an adverb has a number of different meanings.
Thenmeaning ‘at that time’
We can usethento mean ‘at that time’, referring either to the past or the future. In this case, it is usually at the end of the clause:
A:When I was a child, I lived in Austria for a while.
B:What age were youthen?
This time next week, I’ll be on a plane to Kiev. Where will you bethen?
Thenmeaning ‘next’
We can usethento mean ‘next’:
He opened the door,thenthe lights came on and everybody shouted, ‘Happy Birthday’.
Heat some olive oil in a pan,thenadd some chopped garlic and some salt.
Thenmeaning ‘in addition’
Especially in speaking, we can usethento mean ‘in addition’:
Hiring a car is an extra expense on holiday andthenthere’s the cost of insurance.
Here’s our bedroom andthenwe have two more bedrooms down here.
Thenmeaning ‘in that case’
We usethenwithifto talk about cause and effect:
If we buy Jason a present,thenwe’ll have to buy one for Isaac too.
If you are interested in food,thenyou will love this book.
In informal speaking, we often usethenat the end of the clause meaning ‘in that case’:
You don’t want anything to eat? Okay. So I’ll just get you a coffeethen.