How can a new user join the chatroom in XMPP server?

I have established the connection to XMPP server. My question is if there is a Chat Room and new user wants to join, Should I user below Smack class to get it registered?

AccountManager accountManager = AccountManager.getInstance(connection);
accountManager.createAccount(username, password);

Will it create new users to join Room or will it create new user to Main Server. Please help to understand. Thank you!

Mentioned class and method createAccount create new account on server as you can read from the Github code:

https://github.com/igniterealtime/Smack/blob/master/smack-extensions/src/main/java/org/jivesoftware/smackx/iqregister/AccountManager.java

Code:

/**
     * Creates a new account using the specified username and password. The server may
     * require a number of extra account attributes such as an email address and phone
     * number. In that case, Smack will attempt to automatically set all required
     * attributes with blank values, which may or may not be accepted by the server.
     * Therefore, it's recommended to check the required account attributes and to let
     * the end-user populate them with real values instead.
     *
     * @param username the username.
     * @param password the password.
     * @throws XMPPErrorException
     * @throws NoResponseException
     * @throws NotConnectedException
     * @throws InterruptedException
     */
    public void createAccount(Localpart username, String password) throws NoResponseException, XMPPErrorException, NotConnectedException, InterruptedException  {
        // Create a map for all the required attributes, but give them blank values.
        Map<String, String> attributes = new HashMap<>();
        for (String attributeName : getAccountAttributes()) {
            attributes.put(attributeName, "");
        }
        createAccount(username, password, attributes);
    }