Greenbean

I have a 2003 Forester. I want to get the cross bars for the side rails that are on the car already. How do I make sure I'm getting the correct cross bars for the rails? I've already done a basic internet search and there are no clear answers. I don't even know what to call the type of rails my 03 Forester has that would help me know what cross bars to attach to them. Can anyone shed some light on this for me? Thank you.