Usage:FILTER CHANNEL <setting> [option]

ADMIN - Only admins can set channels +L
ALL - All users can set channels +L
CHANOP - Controls who can set a channel +L
IRCOP - Only IRCOps can set channels +L
LOCAL - Local filtering options
NONE - Turn off channel filtering
REMOTE - Remote filtering options
SA - Only Services Administrators can set channels +L

These commands set the levels for the filters as well as who can add the filter mode for channels (rooms). A room filter mode is +L and can be added by either a network operator, services admin, or server admin. Also it sets whether all messages will be filtered or only some messages. The local setting will have it filter messages only on your server, whereas remote will cause it to filter all messages regardless of their origin on the network.

/as help filter channel <topic>

If warn is off, people might not realize when they are being censored or having their messages dropped. Even with warn on they will not be told which word triggered the filter, but unless you have unusual filters it should be fairly obvious. But the warning gives them an opportunity to rephrase their message until it can get through completely.