The AJOIN command is a server-side command that keeps track of the channels you join each time you connect to Digital IRC. If you login with your nick and identify with your password, you can join all the same channels automatically. It works no matter what client you use or where you connect from since all the details are kept on the server.
Registering your nickname on Digital IRC provides a number of benefits. The most notable of these is that registering your nickname prevents other people from using it. Once a user starts using the nickname, they will be asked to ‘identify’ to it with a password. If they fail to do so, their nickname will be changed. This helps to stop people posing as you.
Every channel is able to be private (+p), and/or secret (+s). The two modes are similar, but it is possible for people to find out about a channel that is marked private only (+p). Therefore, if you want a channel nobody will be able to find out about unless they’re told, it is recommended that you mark it as secret and private, +sp. Unless you are in the channel or an IRCop, the server will pretend that the channel doesn’t exist.