In a project, click "client details" and click "create or add a new contact." You can add multiple contacts to a single project and even contacts from different client organizations. Each client contact will receive project notifications and any future surveys you send to clients on that project.
This displays any client contacts associated with your project. You can add as many contacts as you like, start by clicking the dropdown.
"Create New Contact" allows you to create a new client user (who is not already in your EduSourced user list) and add them to the project at the same time.