For entering server : "/server <server name>"
For joining a channel : "/join #channel-name"
For setting nick : "/nick <desired nick>
For registering nick : "/msg nickserv register <password> <your email>"
For identifying yourself : "/msg nickserv identify <password>"
For leaving a channel : "/leave"
For reconnecting : "/reconnect"
For disconnecting : "/disconnect"
Sometimes some shortcut commands also work for identifying yourself, like:
/ns id <password>
or
/ns identify <password>