Inevitably, you have reached the part about "IRC Operators". Oper status grants some special privileges to a user, like the power to make the server break or (try to) establish a connection with another server, and to "kill" users off IRC. I could write many pages about this; I will restrict myself to say that if you want to point somebody as IRC Operator on your server, that person will be aware of his/her responsibilities, and that you, as the admin, will be held accountable for their actions.
There are two sorts of IRC Operators: "local" and "global". Local opers can squit, connect and kill - but only locally: their +o user mode is not not passed along to other servers. On Undernet, this prevents them from using Uworld as well. Depending on some defines in include/config.h, local operators are also not allowed to /DIE and /RESTART the server.
The operator's nickname.
The host or IP mask that will be autorized to use the Oper status.
The password is encrypted so it can't be retrieved by viewing the configuration file.
To change the password you only need to rewrite it and the password confirmation, if you don't want to change the password but only some register of the operator, do not write anything in the password field.
Leaving Global checkbox unchecked will only give local operator to the current operator.
Notice that the connection class is optional, but leaving it away puts the O: lines in class 0, which usually only accepts one connection at a time. If you want users to Oper up more then once per O: line, then use a connection class that allows more then one connection, for example using class 10.