How to fix an image to right side of screen

Hello there,
Just a quickie that I hope someone can help with.

I like the "Follow Us" badge on the below website. It has been glued to the right hand side of the screen and it stays in view even if you scroll down the page.
http://tillison.co.uk/

I'm assuming this is a CSS function but I wouldn't know how to go about making one for my website.

So, can anyone provide any help/code on how to achieve this?
Thanks in advance for any help offered.

Mark