To see the drastic design differences between Win8 and Win10 apps, you don't have to look farther than first party apps, such as the News app...
Windows 8 News App
Windows 10 News App
As you can see, the metro-like concepts such as horizontal scrolling, slide-out menu options and mandatory full screen have been abandoned for vertical scrolling and *ahem* hamburger menu navigation.
So, as an App Developer, where do you go to get a "quick start" or guideline for UWP? Here are a few resources that I found useful.
- UI basics for UWP apps breaks down the parts of an app from a high level, but stops short of code examples. Still a good idea to read through this though!
- Navigation menu (XAML) sample is a concrete example of the Hamburger Menu integrating with navigation. I used this as a starting point for porting my app.
- Template 10, while I chose not to use it, offers a more fleshed out starting point for a XAML-based UWP app. I started poking around with this, but it appears to be still a Work-in-progress at this point and had a bit more than I needed for my app conversion.