Either use the Organizations and project menu
or the "+" sign
Next, click "Add Member" and type the email of the team member you wish to invite and assign them the correct permission level, and projects (if they are a read/write member).
Read/Write members can create user scenarios, data stores, test configurations and execute test runs for assigned projects.
Admin users have full access, like the account owner.
Once finished, click "update organization".
If you have any difficulties adding team members, please let us know.