NickServ is a network bot that manages users and nicknames on IRC. If you register with NickServ your nickname will be protected so that no one else can take it. You can also get auto-voice and auto-op when you join a channel, and you get access to MemoServ to send and recieve messages to users who are offline.
You can also ask NickServ for help:
/msg nickserv help
To automate logging in/identifying to nickserv when connecting try Info/IRC/SASL