Usage: AUTH <command> [<parameters>]

This command is used for adding a nickname, or channel privilege to your buddy/watch list.

ACCEPT - Approve the authorization request and memo the person confirmation.
APPROVE - Same as accept.
DECLINE - Decline the authorization request and memo the person that you will not be added to that buddy list.
LIST - List buddy requests.
READ - Read the AUTH request Message.
REJECT - Decline the authorization request without memoing.
VIEW - Same as read

/msg nickserv help auth <topic>

If you are on someone's buddy list then they will know when you are on the chat network. If you are informed that you have a buddy request waiting for you, use the list command to see what its number is. Then read it by using the read command with its number. If you wish to allow the person who sent it to add you to their buddy list then use approve or accept with the auth number. If you do not want to be added to that person's buddy list, use decline or reject.

Other related commands:
/msg nickserv help buddy
/msg nickserv help set authorize