As well as being able to chat on public channels, mIRC also allows you to chat privately with other people.
If you are on a channel, and you see someone you would like to chat with, you can double-click on their nickname in the nickname listbox and a private query window will open up. You can then start chatting privately to them through the query window. Alternatively, you can click your right mouse button on a nickname in the nickname listbox and a popup menu will appear with various options, one of which will be to open a private query window to the selected nickname.
If you are not on a channel, you can type the command /query nickname, where nickname is the person you want to chat with. Press the enter key, and a query window will open up and you can start chatting privately, assuming of course that the person is on IRC. You can find out if a person is on IRC by using the /whois nickname command.
There is another way to chat privately called DCC Chat. This method is more secure and usually faster because it does not rely on the IRC Server to relay your messages. Instead it connects directly to the other IRC Client. However it does need to use the IRC Server to initiate the chat session.
To DCC Chat with someone, click on the Chat button in the toolbar, and a DCC Chat dialog will pop up. Enter their nickname, and click on the Chat button, and if they accept your DCC Chat request, you will be able to start talking to them in private.
If someone sends you a chat request, a chat dialog will pop up asking you whether you want to accept their chat request. You can then accept or decline. You can find out more about DCC Chat related settings in the DCC section.
Note: DCC Chat needs to use your IP address to initiate a connection with another client. If you are having trouble initiating a connection then your IP address might be wrong. See the Local section for more information.