The forge documentation is there mostly to just get you started, and explain some key terms/ideas. I don't think they meant it to be a how-to or to teach people how to accomplish specific goals within their mod.
There's is a community wiki that was being used, I have no idea if it will be updated/maintained going forward, that has a little bit more/other information: https://forge.gemwire.uk/wiki/Main_Page
Also McJty goes into some detail on some common goals people have while creating mods: https://www.mcjty.eu/docs/intro
Beyond that, the best advice I have is to look at the code of other mods, and even dig through the minecraft code itself for ideas of what's available for overrides/properties/etc., and tinker with stuff constantly