adding information to a column from another columns/table

I have a list of orders, with order number, values etc. each on rows and need to add there also the country of the buyer. I have another list with two columns, order number and the country of the buyer next to that. So I would need to be able to add this country information to the correct row of a matching order number in the main list. How to do this, it is very slow to manually fill in and compare the lists.