A Microsoft platform for building and publishing apps for Windows devices.
You start small and build on what you learn.
Start by building a "Hello World" app. Learn how to navigate Visual Studio. Learn how events work. Add some controls to your app. See how they work. Learn how to compile the code.
Find sample projects on the net. Compile them. Play with them. Make changes to them.
Take a course at a local school that teaches C# programming with Visual Studio.
Luke, you keep asking very open ended, non-specific questions. Like how to build a Google Earth type app. This appears to be one of those occasions where, if you have to ask these questions, then you likely don't have the experience needed to build such an app.
If you are just learning how to program, start with basic functionality first.
https://learn.microsoft.com/en-us/samples/browse/?languages=csharp