After you have customized your “Send Introduction email”, adding a client is as simple as adding a User to WordPress. When logged into your WordPress install go to the Users tab, click Add User and fill out the info on your user.
DO NOT CHECK the “Send User Notification” option if you are going to use the Client Introduction feature. If you decide to use the Introduction Email option make sure you have checked the “Send Introduction email” before clicking the “Add New User” button.
After the page is successfully saved the Introduction email will be sent to the new user. See example photo below.