Either use the Organizations and project menu
or the "+" sign
Next, type the email of the team member you wish to invite and assign them the correct permission level.
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.
Finally, assign the team member to the project(s) you want them to participate in/work on by using the third column's multi-select drop down. Once finished, click "update organization":
If you have any difficulties adding team members, please let us know.