After creating a new client organisation you need to create the users at that organisation. For existing client organisations you might have to add new users.
- Log on as admin user
- Select your organisation from the 'This User's Organisation' link on the top left
- Click on the 'Client Organisations' tab
- Select the practice you want to add users by clicking on the practice name
- Click on 'Add new User' and fill in the details on the next screen, then click save