An account user is an account owner, the person who registered for an account with QuickBlox. In other words, the account user is a QuickBlox customer.
API Users are your end users who use the applications you created using the Dashboard, API, or SDK methods.
An API application is the application you create in the QuickBlox Dashboard.
Sign up here if you wish to create a new QuickBlox account.
Feel free to check our official documentation for more information that will help you to integrate QuickBlox services into your applications / projects or contact our Support team by submitting a ticket if you have any other questions.