From a great blog article on hubspot...

1) Go to Pinterest's Widget Builder and select 'Board Widget.' 

step_1

2) Paste the URL of the board you'd like to embed. Customize the size of the board as you wish under 'Advanced Options.' Then, click 'Build It!'

 step_2

3) Two snippets of code will appear. Scroll to the bottom snippet of code, and click 'Advanced' under 'Load the JavaScript.'

 

4) Copy the code from this section wherever you like in your blog post or website. 

Do not paste this snippet more than once! This is the code that allows all of the embeds to load on the page. 

 

5) Scroll up, then copy and paste the code from 'Insert the Link.'