Here are some point that gives the quick overview of ASP.NET.
ASP.NET provides services to allow the creation, deployment, and execution of Web Applications and Web Services
Like ASP, ASP.NET is a server-side technology
Web Applications are built using Web Forms. ASP.NET comes with built-in Web Forms controls, which are responsible for generating the user interface. They mirror typical HTML widgets like text boxes or buttons. If these controls do not fit your needs, you are free to create your own user controls.
Web Forms are designed to make building web-based applications as easy as building Visual Basic applications.