You've probably noticed some re-organization in the fluff and fictions sections.
Here's how it works in here:
The main forum is for discussing Canon (official) GW fluff from the codices and asking questions about non-rule stuff in the 40k universe. "How long do Marines live?" "What was the name of the Salamander Primarch?" etc
There is a new subforum
for posting your homebrew fluff, chapter backgrounds, etc.
If you want to talk about 40k novels and comics, then go to 40k Fiction
If you want to write any short stories and the like, anything that's made up by you but NOT chapter fluff, take it to the 40k Original Works
And, finally, if you have *rules* for your new army/character/codex, you can post those over on the Houserules and Homebrews