How to create child browserwindows?

[bikutaa-dev]

been searching around but can't seem to find any info about it, clearly you make a new browser window, but where should I point the browserwindow.loadURL() to create a second window with another file as the start, and to make it work in bot dev and prod? should I be using "process.env.APP_URL"? any attempt using that just load my main window in the child window.

The second file I want to load is in the /src folder.