/oper and /user

[Huseyn26]

I Know /oper command is for IrcOps.But I Dont Know What is /user,and how to enable it.
Please Say About This

[Stealth]

USER is part of the protocol and is already enabled. The command is used as part of the connection process and may not be used once connected.

Command: USER
Parameters: <username> <hostname> <servername> <realname>

The USER message is used at the beginning of connection to specify
the username, hostname, servername and realname of s new user. It is
also used in communication between servers to indicate new user
arriving on IRC, since only after both USER and NICK have been
received from a client does a user become registered.

Between servers USER must to be prefixed with client's NICKname.
Note that hostname and servername are normally ignored by the IRC
server when the USER command comes from a directly connected client
(for security reasons), but they are used in server to server
communication. This means that a NICK must always be sent to a
remote server when a new user is being introduced to the rest of the
network before the accompanying USER is sent.

It must be noted that realname parameter must be the last parameter,
because it may contain space characters and must be prefixed with a
colon (':') to make sure this is recognised as such.

[Huseyn26]

when i type /user (myusername) (myhostname) (theservername) (andrealname)
i get that: you may not reregister

[katsklaw]

when i type /user (myusername) (myhostname) (theservername) (andrealname)
i get that: you may not reregister

You seriously need to re-read what stealth said. He said it can NOT be used after you connect. The user command is sent by your client when you connect and you have zero control over it.