There are two ways of creating an owner, from the property page or the Owners menu.
From the Property Details page, scroll down to the Management section and create the owner by clicking on the "+" sign. Add all the required fields (with an asterisk) and click "Add". The owner will then be automatically created in the Owners menu and assigned directly to that specific property.
Or, from the Owners menu, click on orange "+" sign and fill all mandatory fields. You can also add Notes and Documents if any. Once you've finished with all the details, hit the green update button to save your changes.