Once you install the ZoIPer, you will see this interface when launched on your computer.

Click on the and it will bring you to the SIP Accounts overview.

Click on "Add a new SIP account"
Key in the required information and click OK.

Click on “Apply” and “OK”.
If the ZoIPer is working, you should see this status (Registered):

You should be able to make call now.

Note: If you require proxy put a check on the "Show Advanced Options" and on the “Use outbound proxy” see sample below.