How to add reference app.config file dbconnection file from class file in C#

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C#

i have included the the dbconnection and config files in my c# project folder(MyProject) to connect sql server



but I got the follwoing errors

Severity	Code	Description	Project	File	Line	Suppression State
Error	CS0246	The type or namespace name 'DBConnection' could not be found (are you missing a using directive or an assembly reference?)	LabProject	C:\Users\Sarvanan\documents\visual studio 2015\Projects\LabProject\LabProject\App_Code\DAL\DataAccessObject.cs	21	Active

How can add the references of dbconnection file

What I have tried:

MyProject
   References
       Class
         DBconnection.cs
   App.config