To add the pinterest function to your web pages and galleries you add two pieces of code. One to the BODY-end text area at My Websites > Embed HTML in other Sites and the other as a widget to your pages. or if you want it on all pages and galleries to your footer or advanced header .
First copy this to the BODY-end:
Now create a new widget with this code:
<a href="//pinterest.com/pin/create/button/" data-pin-do="buttonBookmark" ><img src="//assets.pinterest.com/images/pidgets/pin_it_button.png" /></a>
Further help is available on widget from help article: Using the Widget Library.