Thanks for writing in!
In regard to add yummly button to your post or page; just select your page or post on which you want to exhibit the button and then edit the page. On edit screen, while choosing the text editor (see: http://prntscr.com/a0ypq5), please paste the following code to your text editor:
<a href="//yummly.com" class="YUMMLY-YUM-BUTTON">Yum</a>
Hope this helps.