Once you can grab the html code from Pinterest (I believe it is under "Pin it Button" from the About dropdown menu), you will want to add it to your website through the html element. Please check out adding html for instructions. Once you add the code from Pinterest, move the html box to where you would like the button to appear.
This is the easy part however, there is an additional piece of script that must be added to the page(according to pinterest it needs to be placed just before the ending tag)
Where do I add this html? I've tried adding it through the html element however this does not work. When the page is published and the "pin it" button is clicked it simply takes you to a "create a pin it button" page.