Navigate to Settings > Staff and click Manage Staff in BrightHub at the top right:

You will then be directed to BrightHub on the Members page > Click the Invite button on the top right to add a invite a new staff member. 

You will then be asked to Enter the Email address for the new Staff member and their role. Then assign them to the Product you want them to work on. Click "Send" to send the invitation email to them. 

The new staff member will get an email asking them to accept the invite > Then click the Accept Button in the email and it will then ask them to Sign in by Entering their Email address and a password. 

Note - You can still further restrict specific product access for staff members within the staff screen in Brightmanager