Custom facet display

So I’m trying to build a custom facet display. The docs say one thing, it doesn’t work. I’ve run into the same problem with other docs relating to a different topic and it wasn’t until support made it clear that there was an edited line of code, that I was able to render the widget. What is the best way to render a custom facet display? What files do I edit? Any and all suggestions are a great big help.