Unless you're a designer, you'll find it easier to create a visual application using Windows Forms than WPF... though WPF is the "newer" interface (and the one SSDR uses).
The MSFT online tutorial isn't bad:
Once you've started to play with C#, I think you'll be hooked. It's soooo easy to create a GUI program it's almost scary.
For help with the FlexLib API, just come here and we'll help you out!
The Big Yellow Book of C# is where I started with C#
And.... here are some WPF Books - not sure of the legality of this site, but I normally download them from Amazon and pay for them if a book good enough. Don't like taking food out of a good authors mouth! :-)
When we started there were a lot of good books. We bought some and passed them around the office. I would just go to Amazon or Nerd Books and see what has high marks today and buy one. WPF is quite a bit trickier than Windows Forms for several reasons. You really should spend a little time studying the MVVM (a.k.a. MVC) pattern and internalize it before you start coding in WPF. Understanding XAML (pronounced "zamel" and rhymes with camel) is also important, but you can get by at the start without too much knowledge of XAML.
The world of software has transitioned to this model with UIs for IxD, reusability and separation of concerns reasons and I would recommend investing the time in WPF if you want to understand this new world. The applications look better and you'll be up with current technology. It would be tough to convince me to do much of anything in Windows Forms today.