By default, all the users added to your Organization will have access to all the projects within it.
To invite new users, click the Sharing link under your profile menu on the Project dashboard page.
For every invited user, there are 3 types of roles available out-of-the-box:
Admin – can invite other users and change the Organization settings.
Editor – can view and develop projects.
User – can view and use projects in the End-user mode, cannot modify or develop projects.