Using xlf files in Trados Studio 2015

Hello,

I know that there have been previous discussions on this topic but it is still unclear to me how to proceed.

A client has sent me an xlf file and the xls source file, I have no idea how to use the xlf file with Trados 2015.

Could some please explain how to use this file type with Studio 2015?

Many thanks in advance,

Michelle