So basically, thanks to @Blender, the information is available at https://github.com/dockimbel/Red.
I knew I saw the information before, but I couldn't remember where. I checked the "Docs" folder in the Red distribution, but that didn't have the information there (might be handy to add it).
- Start the Rebol interpreter in the folder where the Red files and folders are stored.
- For Red:
>> do/args %red.r "%red/tests/console.red"
- For Red/System:
do/args %rsc.r "%tests/hello.reds"
See the link for more detailed instructions.