What is the purpose of a .edmx file?

What is the purpose of a .edmx file? It is a XML formatted file in Visual Studio. It has database table information. But how is it used in a Visual Studio C# asp.net web app?

Online search engines say that "an .edmx file is an XML file that defines a conceptual model, a storage model, and the mapping between these models. An .edmx file also contains information that is used by the ADO.NET Entity Data Model Designer (Entity Designer) to render a model graphically."

But how is it used, and how is it made?

Search for "ADO.NET Entity Data Model Designer "

It's an Entity Framework file. It gets created when you do a design first EF implementation. You can create one with Add New Item/Data/Ado.Net Data Model. You can choose to create the entity model from scratch or point it to an existing database and have the model automatically created for you.

Once the model is created you can use it to save and retrieve data to/from the database (and much more).