The properties is a simple key/value store of values which can then be used as part of your deployment.
If a property has already been defined either as an environment variable or a duplicate value in your deployment configuration file the 1st value found will be used.
Properties can contain dynamic content using the template tag syntax.
<Structure xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
...
<Properties>
<Property name="Key1">Value1</Property>
<Property name="Key2">Value2</Property>
<Property name="KeyWithDynamic">{{ ClientCode }}-Value</Property>
</Properties>
...
</Structure>