When a single customer has multiple properties being serviced by you, you'll want to create all of those properties on the same customer instead of creating multiple customers for each property.
How to Add an Additional Address for a Customer
Navigate to the Customer page
Click the Locations tab (map markers icon)
Click "+ Add Address"
Start typing the address you want to add and select it from the list that automatically appears. Click "Add" to create the new address.
How to Edit Existing Properties
Navigate to the Customer page
Click the Locations tab
Hover over the address you wish to edit
Click the blue Edit pencil
Make the necessary edits (address spelling, tax rate, etc)
Click Save