This is a very broad topic to cover in a single answer and requires a very long answer for a clear response. Read this article of mine,
How to connect SQL Database to your C# program, beginner's tutorial[
^] as the answer to this question of yours.
You will get all of the related information about SQL Server (Express) and namespaces and other objects provided in .NET framework (using C#) which are to be used in working with SQL Server in .NET framework. You can use any framework of .NET applications (Console application, WPF, Win Forms).