what do you think i need to use to build a web app for books . like a labrary . (with c#) ?

Question

c# is already choisen

Answer 1

Hello!
You should use ASP.NET framework for building web apps.
I recommend you use ASP.NET Core MVC which is easy enough.
Also you should use Entity Framework for communicating with Microsoft SQL server which will hold databases.
Some links:
1. ASP.NET docs
https://docs.microsoft.com/en-us/aspnet/tutorials
2.ASP.NET Core MVC guide
https://docs.microsoft.com/en-us/aspnet/core/tutorials/first-mvc-app/?view=aspnetcore-2.1

Happy Coding! ;)