Hi, there’s nothing to do to use it 
You just edit in wiki mode.
However I don’t know how well it works or if it works at all. As you can see (on https://extensions.xwiki.org/xwiki/bin/view/Main/ or in the Extension Manager of your wiki) it’s not a recommended extension and it’s not developed by the XWiki dev team so we can’t guarantee it works.
I’ve tried it quickly and it doesn’t work for me. I got an error message:
Note that you need to open a port if you’re behind a firewall, see the doc at https://extensions.xwiki.org/xwiki/bin/view/Extension/RtWiki#HPrerequisites26InstallationInstructions