The question makes no sense. And it has nothing to do with WPF. A property is a property. If your question is about some particular property, you could at least provide some link or code sample. But this is not what you really want. You just need to know how to do programming, in particular, with properties.
The property is set by using assignment operator, =.
Please see:
Properties (C# Programming Guide)[
^].
By the way, for understanding WPF in depth, you will need to learn
dependency properties and
attached properties, but these topic are hardly related to your question. If you are interested, you will find the links by yourself.
—SA