Reactions are an easy way for your readers to leave feedback on your blog without leaving a comment.
You can add a reaction by clicking Layout, and then Edit on the Blog Post widget.
The Configure Blog Post window that pops up will display a handful of options, and the Reactions feature is near the bottom of the list:
To turn on Reactions just select the checkbox, and then you'll be able to customize the feature by adding words of your choosing. Finally, you can choose the exact location of Reactions by dragging the widget at the bottom of the Configure Blog Post page: