To add custom property "Country" to an entity (for example, the "Customer" entity), connect to your database in Configurator, expand Entities, expand needed entity, right-click on Properties and select the Add Property option: 

In the Property Settings area, enter the name of the property and select Country as its Data Type:

Save and commit the new property settings:

Now when you start CentriQS Client, the property Country will appear in the detail view and main view of the Customer entity: