Inserting a fine line

Hello,
Please firstly understand I don’t understand code, new to website building and all that. But I’m really enjoying myself.

Please tell me how I can insert a fine line beneath my logo and menu but above my slider – pretty much the same as your Site Origin page. I use my home page as the template for all my pages and because I’ve just moved the menu up there, there’s a little too much “blank space” underneath.
Thanks
Andrew

URL: http://www.ridgestone.co.uk