you can use TextBlock control and assign the text property.
Label myLabel = new Label ();
myLabel.Content = "Hello World!";
In normal winForms, value of Label object is changed by,
myLabel.Text= "Your desired string";
But in WPF Label control, you have to use .content property of Label control for example,
myLabel.Content= "Your desired string";
You can use the Content property on pretty much all visual WPF controls to access the stuff inside them. There's a heirarchy of classes that the controls belong to, and any descendants of ContentControl will work in this way.
I believe you want to set the Content
property. This has more information on what is available to a label.
Source: Stackoverflow.com