I do not seem to be able to get the Rocket Chat running. Correctly. Some can help me to find a step by step instructions, please? with my 60+yrs I seem to be lost here a little.
I installed it on my site at xsimracing com / XSIM/ but this Rocket Chat does not work.

RocketChat requires to be installed at the root level.  First determine what your OS is on the server and then go to rocket.chat and you can find detailed instructions for your OS on how to install it.  You also need to set up a reverse proxy on your webserver; that can be tricky sometimes.