If you want to bypass the process of a member joining your site and simply invite someone (say someone who is already in your guild and does not need to apply to join), you can do so by going to the Roster section of your site and clicking the "Invite Member" button:



From here simply enter their email address and the name they should be displayed as, and a member will be created on your site for this user and an email sent out to them for them to setup their account.