WPF or Windows Presentation Foundation is part of the Microsoft .Net Framework for designing graphical user interface.
At its core is a set of XAML based language that we use to design the desktop UI. XAML is a declarative markup language just like HTML.
WPF was released only in 2006 and prior to that, we have been using Microsoft Foundation Class and WinForms to design the user interface.
With XAML, it makes designing user interface more like using HTML to design a web page and its user interface.
Since 2006, Microsoft has been improving WPF and now you can do most things in WPF without resorting to using WinForms.
When you first started learning WPF, you could be easily overwhelmed. There are just so many little things to take care of.
Now, when I compare using WinForms and Foundation Classes, I am just glad that we are now using WPF which is a lot more easy.