Hi KatieNgoc,
In Solution Explorer in project node choose Add New Item.
In the Add New Item dialog box, choose the Resource File template, and then select the Add button.
As soon as you add the first Resource file you will get the prompt from Visual Studio asking to place the file in App_GlobalResources.
You need to click Yes.
Once the Resource files are added, you will able to see the Resource files in App_GlobalResources folder in the Solution Explorer.