How can I freeze the header section?

I'm interested in creating a header that stays frozen in place, no matter where the user scrolls on the page ... not sure how though and the theme developer wasn't available to help as it's more programming work than support.

Thought I'd ask you fine folks :slight_smile:

It's a shot in the dark, but I'd really love to achieve it so any ideas are appreciated.

Example of what I'd like to achieve:
http://www.shopify.com/

My site:
http://wearabl.com

Screenshot attached:
What the header looks like while visitor scrolls down the page.

Ideas?

Thanks for all your support everyone. Cheers!