Mail and GMail Issues

Hi - Trying to add a Gmail account to a MackBook Pro mail app but constantly receiving the following error message despite logging correct details.
Logging in to the Gmail IMAP server “imap.gmail.com” failed. Make sure the user name and password you entered are correct, then click Continue. If the information isn’t correct, you cannot receive messages.

Access the gmail IMAP and POP trouble shooter and follow directions for Apple Mail. The link is here.

This will probably come up in the troubleshooter, but you have to go to gmail settings (meaning account settings in gmail via browser) and tick a box to enable imap. If you havent used a gmail account with a client, then you probably have never done that.