Gmail Email Inbox using PHP with IMAP

Warning: imap_open(): Couldn't open stream {imap.gmail.com:993/imap/ssl}INBOX in /var/www/html/mail_inbox/mail.php on line 12
Cannot connect to Gmail: Can not authenticate to IMAP server: [AUTHENTICATIONFAILED] Invalid credentials (Failure)
Notice: Unknown: Retrying PLAIN authentication after [AUTHENTICATIONFAILED] Invalid credentials (Failure) (errflg=1) in Unknown on line 0

Notice: Unknown: Retrying PLAIN authentication after [AUTHENTICATIONFAILED] Invalid credentials (Failure) (errflg=1) in Unknown on line 0

Notice: Unknown: Can not authenticate to IMAP server: [AUTHENTICATIONFAILED] Invalid credentials (Failure) (errflg=2) in Unknown on line 0