If you want to add someone new to your account, you can do this by selecting the Account tab and then Add New Users. You can then add their email address.
By selecting from the Access Level drop-down menu, you are deciding the permissions granted to that account user. A manager can only view and edit reports they create. You can also assign pre-existing reports to managers for them to view and edit. An organisation admin can view and edit all reports in the IG Tools account.