I set 3 environments ( Debug, Stage and Production ) and created a custom variable with a name testVariablefor each environment on the RELEASE tab of my Visual Team Team Team Project, as shown here:

I also have a release variable with a name testReleaseVariableshared by all enviornments, as shown here:

I cannot find documentation on how to configure my ASP.NET projects in VS to use these variables when developing locally, as well as when deploying the assembly, so that they can be entered by the release manager.
ASP.NET 4.5, ASP.NET 5.0. : Web.Config( ASP.NET 4.5) Config.json( ASP.NET 5) , VSTS.