When opening the app you will be presented with an Add Account option in the middle of the screen, select this to bring up the Choose Wizard menu. Select Basic.
Once on the Basic wizard you will then see the account settings page. Fill in the account name with what you wish to call the account (this is personal and can be anything).
The Authentication details can be found within your control panel. The Server will be the SIP Proxy, the User is the Username, and the Password is the Password.
Once the credentials have been entered and saved the accounts page will show the account you've just created and say Registered.