src/App.js

So I am working through this article. I am currently on the 3rd step where you open the src/App.js in a code editor on your computer. However, I have no idea where this file is. I cannot seem to find it anywhere. I am assuming it was created when I installed everything and started the new app. The thing is, I cannot find any of it on my computer. I am using a Mac and am running the latest version of the OS. Could somebody please help me figure out how to locate this file?