There are four user roles with different rights: member, creator, manager, admin.
Members can only work in projects they are assigned to. Creators can create new projects and work in all assigned projects. Managers can see all projects, create new ones and assign exisiting users to projects. The admin is the only one who can invite new users to an organization and handle everything related to the billing of an organization.
Also, if you have two projects at the same time, you e.g. assign 3 users to project A and 3 users to project B so they can only see the projects they have rights for.
To give admin rights to another or a second person, please get in touch with us, we're happy to get this done for you.
You can find more information about multi-user management here.