Answer 1

c# and vb.net are programming languages based on the .net framework.
c# can be used in writing apps for PC, iOS and Android(xamarin) and also used in coding asp.net pages as well as embedded systems programming
VB.net can be used to build apps for PC and coding asp.net pages ... it can be used to do basically everything c# can do.
the main difference between c# and vb.net is basically their syntax. they do pretty much the same thing as they are stripped down to bare syntax with all additional services moved to the .NET framework class library, which is common to most languages
ASP.net is a .NET technology for building web applications.
c# or vb can be used in programming asp.net pages