The only option required from this screen to make the softphone work is the Accounts button. All the other options are personal to your own requirements from the phone and will rarely be needed to get Zoiper working with your VoIP account.
After selecting Accounts you then need to add an account by tapping the + symbol highlighted above, then choose SIP account and enter your extension credentials:
Account name: This can be set as you wish and is merely for reference. If you’re configuring multiple accounts then it makes sense to set this to something relevant.
Domain: As per your VoiceHost control panel.
User name: As per your VoiceHost control panel.
Password: This is the password relevant to your ext/seat
Network Settings: In this option is another setting titled Refresh which should be set to 60.
With all the above done, come out of the Network Settings screen so your back at the SIP Account screen, scroll to the top and tap Register.