All connections to the server are associated with a certain "connection class", being them income or outgo (initiated by the server), being them clients, servers or Martians. (Notice that ircd doesn't have direct support for Martians); they will have to register as normal users.
all your uplinks for who you do not wish to hub; same in classes
leaf servers (only used if your server is a hub)
for all .net and .com that are not in Europe.
The frequency that the server ping this connection.
I don't know what it really does. I think it is the frequency that this class can connect to the server.
Prevents users to flood connections.
The maximum of connections by the same IP.