These commands allow you to set masks for a client profile. When clients login, they will be compared to the set masks. The first mask they match will control which profile they get.
ADD - Add a Client host mask
DEL - Delete a specified Client host mask
LIST - List all specified Client host masks
/as help client mask <topic>
In order to enter the chat network a user must match one of the enabled client masks. Unless you disable the z-default profile, everyone will match it so everyone can join (unless there are klines or other things blocking them specifically). They will receive the modes and the MOTD associated with the first profile they match. The above example would match anyone from webmaster.com. An addy such as *@*.aol.com would match all AOLers.