need to report a ragequiter

Rage quitting is not punishable. However, if the room is official and he is annoyingly persistent, gather several evidences of him rage quitting and forward it to a gm. Gm will handle the rest.

but, do you know how to report?

Take a picture of what you're reporting, like a scam or someone multiclienting and send the pictures with a description to a Smod or a Admin (Blue or Red names).

Also, there's a section for scam reports etc...

Better read this.
http://forum.toribash.com/showthread.php?t=346542