If you'd like to, you may add a Comment to a post. On posts especially better or worse than average, rather than saying "POTW" or jumping on someone, you can give a thumbs-up or thumbs-down and add a comment for the original poster. There is an icon, (+/- in Mobile), in the lower left part of each post for this. When you float your mouse over it, you'll see "What do you think of this post?" Remember, civility applies here, too!
Comments are reflected in points, and points are reflected in pitchforks by your username. You can only comment on recent posts, only a few times a day, and you have to spread 'em around between different members. You can see the last few comments you've received on your settings page.