After adding the user to the organisation, you can assign a role to that user. This can be done by following the steps below.
1. Click on your e-mail ID on top right corner
2. select "My organisations"
3. Click on the "Apps" button on the right side
4. Choose the "Settings" of the app you want to give access to
5. Click on "Roles" tab
6. Select the user and assign a role (Admin, Developer, Customer Support) from the drop down menu
7. Click on "Add" to finish