The premis of the site is quite simple. People make captions to adorable and funny pictures. Cats, dogs, other animals, celebrities, politics . . . . Another part of the site is their "fail blog". Hilarious!
I stumbled upon this site a few years ago and I check it about every other day! My addiction to it is almost as bad as my addiction to Etsy! 
You can also upload your own pics and make captions for them! How fun is that?!

If you haven't been to the site, you need to go! It's worth it, trust me!