Menu link (extreme beginner!)

Hello,
I need help linking one of my ‘pages’ to another site. I am very new to editing themes and templates! Any help would be much appreciated.

I would like my SHOP menu button to link to another site (an etsy store). Cannot find where to enter this HTML link – I am looking in the Style.css- is this the right place for it?

http://unraveled-clothing.com/

Thanks!