You first need to install the Scheme host that Arc runs on top of. If you're running Arc3, it's MzScheme v372; if you're running Arc3.1, Racket.
Then download and run Arc. I don't have Arc in front of me, but if I recall correctly, you start the news server with (nsv). There's a file distributed with Arc called how-to-run-news, or something like that. Read it; it's quite useful.
You can call (thread (nsv)) if you want the repl to come back so you can make further changes while the server's running.
That'll get it running, but you may have to open up ports in the firewall to let people connect from outside. You'll also need to customize some variables, like the name of the site, and colors, and the favicon.
