To do this you will want to add a link to your blog.
Log into your blog and select 'layout' on the left hand menu. Choose where you would like the link to appear and click 'add a gadget'.
This opens up a window with a list of gadgets that you can add to your blog. Scroll down until you find one called 'picture'. Click on the little plus icon next to it.
Now you can choose an image that you would like to turn into a button that people can click on to view your shop. You could try one of the find me on folksy badges for example. They can be found here - just right click on the one you want and save it to your computer.
View your blog and you will see that you have a fab little button. Click on it and it should take you to your shop. Very nice.
Why stop at one link? If you have an etsy shop as well as a folksy one, add this. Or add links to your facebook page, twitter, pinterest etc., wherever you want people to find you. You can design your own images for these, or take a look at this site - they have lots of free social media buttons that you can download.