These type of applications don’t provide a way to create an account. They’re SIP clients that use PIN, username and password to connect to server to place calls. I have checked the software and there is no way to create an account from interface.
The accounts for these applications are usually found on the pre-paid cards you buy. When connecting through the application, you need to enter an operator number, username and password, and based on these credentials you connect to the available servers to place calls.
To set up an account, install the application, and then use your username and password to log-in through the Settings menu. After this procedure, you can call using the SIP servers and the application.