How to: Add an Application Configuration File to a C# Project
By adding an application configuration file (app.config file) to a C# project, you can customize how the common language runtime locates and loads assembly files. For more information about application configuration files, see How the Runtime locates assemblies (.NET Framework).
UWP apps don't contain an app.config file.
When you build your project, the development environment automatically copies your app.config file, changes the file name of the copy to match your executable, and then moves the copy to the bin directory.
To add an application configuration file to a C# project
On the menu bar, choose Project > Add New Item.
The Add New Item dialog box appears.
Expand Installed > Visual C# Items, and then choose the Application Configuration File template.
3.In the Name text box, enter a name, and then choose the Add button.
A file named app.config is added to your project.