First, change the settings (they are automatically displayed when running mIRGGI for the first time). Input nick, username, realname and server. Press back and then connect.
If you want mIRGGI to connect to channels or open query windows on startup, input them to Auto windows setting. Separate channels and nicks with commas. If you need keys for channels, you can input them too. Example: #channel key,&channel2,nick1,nick2 will open #channel with a key, &channel2 without a key and query windows for nicks nick1 and nick2. These windows are numbered 1-4 and you can use keys 1-4 to quickswitch to them.
NOTE! Disconnecting and connecting or connecting after network disconnection might not work. Close mIRGGI and start again. Yes, this will be fixed.
To input text, press enter or OK button. This will bring the cursor to the input line at the bottom of the screen. Press enter or OK to send the line/command. If you don't want to type anything, pressing OK/enter on an empty line disables inputting. If the line starts with / it is considered a command, otherwise the text is sent to the channel or query target.
When not inputting text, left/right change the windows. Also pressing 0-9 will jump to that window (0 is always the server window, channels and queries start from 1). Up/down will scroll the current window. At the moment, the window scrolls down when new text arrives. I know, this can be annoying sometimes.
Windows are created when joining to a channel or starting a query. They are not closed if you leave a channel at this time. You can use /cquery command to change the nick in the current query window if the other party changes their nick.