In order to import Users for your account how over My Account in the top right and click Manage Users.
Select the orange Import Users button.
It is recommended to download the sample CSV and fill it in with your information rather than attempt to create the CSV by hand. The only field that MUST be unique is the Username field (it cannot overlap with any other RAP user, even those outside of your account). Select next and browse to your saved CSV and click next once more.
The app will then review your results and show you a list of all Users being made, as well as any conflicts or issues with the import. Press confirm to finalize the import.