First of all, please understand that there is a difference between mIRC (a chat client) and an IRC network (a collection of servers that run an Internet Relay Chat system).
mIRC allows you to connect to hundreds (thousands?) of IRC networks. However, while these networks are all broadly
the same, there are differences between them. Some, for example, have no services at all, meaning that to maintain a channel you need to have a client or bot online all the time. Some have services like NICKSERV, to which you can authenticate yourself to prove who you are, and CHANSERV which maintains a channel for you.
Because every network is different, and some have no services at all, there is no standard answer to your question - which is why it can't be put on the website or in the FAQ.
The details of how individual networks organise themselves (services etc.) will probably be found on the network website.
For help with nickserv (assuming that the network you are on has it), you could also try typing the helpful 'shortcut' command /nickserv help
in mIRC, or you could drop into a help channel (usually #help or #beginner) and ask the friendly helpers there