They're comics made about the community in humorous ways for the most part. The characters used for the users are based on avatars and what character that person is sort of known to like or use as a theme. [For example, I'm known to spam Pokemon art regularly and I have had this character as an avatar for a year and a half, so I'm guessing thqt is why
Fawn picked him, hope I'm making sense. Fhant is also literally a box, and others are based on old Chuu characters] Anyone is welcomed to be in a Chuu or make one, but I do recommend reading a thread Merun made for them first. I remember being confused about them too for awhile, so I understand how you feel now, haha. Some users draw them themselves, and some edit art of the characters [in this one's case]
Some people are sort of known for certain charms they have and Chuu takes a humorous poke at them. Ran loves Shimakaze, Fhant really loves cat girl maids, Biba is shy, I'm. .. a bit of a wild one. Idk. This is literally the second Chuu I've been in. But hopefully that makes sense too.

Here's a better, more detailed explanation.
- http://e-shuushuu.net/wiki/index.php/E-chuuchuu
- http://e-shuushuu.net/forums/viewtopic.php?f=9&t=1617&p=64863&hilit=chuuchuu#p64863
. .. Annnnnd that's what I get for quickly reading a comment. Sorry, missed the pm part. ;;