What is .NET, ASP.NET, looking over them the verbiage is extremely foreign to me.

Okay so I have VS 2015 and tried to develop on it to build some small apps but soon had to drop it for the lack of, well in short understandable tutorials. I am coming from Linux and only using Ubuntu to build my apps with MEAN or Meteor. So to me those seem very native and simple.

When looking for a job all I see online are C# or .NET developers. I tried to learn by going to MS and watching tutorials or going online but I feel like a mouse in a forest trying to find anything. While it seems like a very robust ad mature environment to me a newcomer it's rather daunting. I recently got a web app working using MEAN stack on windows using VS coder.

How does .NET fit into all of this. What exactly is .NET? Is it the backend framework? Does it interfere with the front end. Does anyone know of any tutorials for skilled Javascript stack developers to move over to the C# side? I have looked over C# and it is very similar to Java but am still confused on how VS, ASP.NET, C#, and the front end fit together. I just want to make an API server side and then have a front end like Angular 2 that talks to the API.