Can you help me with ASP.NET?

Question

ASP.NET

I started studying asp.net mvc 5 (I honestly don’t know why, they say that Core is much better, but in our city 90% of vacancies require knowledge of it + ASP.NET Core).
So, just looking at vacancies, I came across the fact that employers indicate in vacancies like the web, but somehow .NET does it there, although up to this point I guessed that ASP.NET and .NET are different things.
Can you break it all down? Is .NET used on the web and is it necessary to learn it to learn ASP.NET?
What is a .net developer? Still on the web part or not? (I'm in a stupor