Client contacts each have their own username and password to the system.
Their email address will be their username, and their password needs to be set by editing each of the contacts details.
Eg. A client 'ACME Group' might have 3 contacts/staff which have been added (Mary, Jane, Steven). To setup a password for Mary, Jane & Steven, you will need to edit each of their details, and set an individual password.
Setup is done in two stages;
They should get an email with their password and some brief instructions on how to login to the client portal. You might want to give your client a call as well to make sure they've received the email and were able to login.
The client portal is located at the following address:
https://<your site url>/client-portal