Used to register a room with services. After registering your room, you will be able to determine how it is run. You can control who may join and how much power each user has. The room will remain yours so long as your nick does not expire and someone is opped in the room regularly (the exact time period is settable). The room will not expire from lack of use if a root sets held on for it, see the root command section for more information on held. Who may register a room is settable by a root. Some networks will allow any user to register a room while others may restrict it to network operators.
/msg chanserv register #support mypasswd Product Support Room
If you plan to talk to a group of people regularly you should register a room in which to do it. It is important to register a room rather than just using a dynamic room so that you can guarantee it will remain yours. Otherwise you might have to switch rooms, and informing people will be tedious. You can also register a room if there is a topic that interests you, but you're not sure who would want to discuss it. Just register a room with a name that implies that topic, say #baseball, and with time people interested in talking about baseball will be likely to join.