Yeah stuff changes on the interweb.
This is the contents of the documentation:
https://www.jamroom.net/the-jamroom-network/documentation/contents
There is a section "Jamroom 4 to Jamroom 5"
and there are a couple of video courses here if you like videos better:
https://www.udemy.com/start-your-own-online-community
https://www.udemy.com/developers-guide-to-customizing-jamroom/
As a brief overview:
Now everything that is part of jamroom runs through the router system. So any incoming url's get funnelled into the the router that then works out who wants to deal with it.
The result is that you don't need to change core files to take control of a location. It works really well.
EG:
For this url your-site.com/somewhere That could be either a .tpl file in a skin called 'somewhere.tpl' OR it could be a module that takes control of the 'somewhere' url.
So the possible locations for output of that page are:
/skins/(YOUR SKIN)/somewhere.tpl (if that .tpl file exists in the skin) OR
/modules/xxSomewhere/templates/index.tpl (if there is a module controlling the url)
Then there are many more levels of possible interaction between modules and other modules.
So yeah it got a bit more complicated in JR5 but it also got a lot more powerful.