I think it's because you aren't following the cats stream.
If that's true, you would only be able to use the "Post a meme" and "Post a gif" buttons circled in red.
Click the drop-down circled in green, then click the "Follow" button circled in yellow. Once you are following the cats stream, you should be able to submit all your kitty related charts and demotivationals from the Submit button on your image pages.
Caption this Meme
