To be an op (@) you need to join an empty channel that has not been registered. Do remember, although Undernet (the network you obviously use) does have channel services, not all networks do. To do this, simply type /join #channel-name
where 'channel-name' is the name of the channel that you want. Popular names such as #mIRC or #Chat are always taken by people who have been on the network for years.
To register a channel on Undernet you need 10 supporters. Login at cservice.undernet.org/live/
and click to register a channel. If you don't meet their requirements (which are not easy) then you cannot register a channel. That is their rules and nobody here can change that.
Either way, provided nobody else registers your empty channel (which is unlikely) you will remain as operator. For help with X commands, go to the #Help or #CService channel on Undernet, or /msg X Help <command>
where <command> is a command you need help with (e.g. /msg x help op).
Remember that mIRC is not affiliated with any one channel, server, service or network. X nor Undernet is not the same as 'mIRC' - you can simply use mIRC to connect to Undernet and use their services. Services are unique to the networks that use them, and you can't always find support here. For indepth services help you'll need to ask on the network you use.
Best of luck!Edited for reasons below