When you've added clients into your system, you can start inviting them to use the system. In the client's profile, you will see the option "send invite". When you click this, the client will receive an email inviting him to join your portal. The email that is sent out, can be viewed and adjusted in the system settings, under email templates. You can use the codes that are displayed to personalize the email and set it up just the way you want it. People will be able to register through the link that's in the email and they will have access to your portal from then on.
Please note that sometimes the invitation email can end up in a client's spam folder. What we suggest is notifying your clients about the upcoming invitation through your own email system first. This way, they will know what to look out for.