These instructions show you how to install River4 on a machine that's never had Node running on it, using the file system for storage. You can also use S3 for storage, and there's a separate howto for that kind of installation.
These instructions assume you're installing on a Macintosh, but they're very close to installing on a Unix or Windows machine.
Download Node.js from this page. Get the Macintosh installer. You don't need the source code.
Run the pkg file you downloaded. Accept all defaults, install for all users. At the end it tells you where everything was installed. I didn't need this information. It also says to make sure /usr/local/bin is in your $PATH. I didn't need to do anything, apparently it was setup correctly by default.
Install the packages River4 needs.
Shortly after it launches, River4 automatically creates a river4data folder in the same folder as the River4 app. It contains sub-folders: data, lists and rivers.
For now, lists is the important folder. Copy a few OPML subscription lists into the lists folder. If you need some to help test your setup, you can download some examples here. Ultimately you'll want to create and maintain your own. Fargo is very good for that, its native file format is OPML. Use the Add Feed command in the Outliner menu.
Let River4 run for a while. As soon as there are new items in the feeds in your lists, river files will show up in the rivers2 folder, one corresponding to each of your lists. These are used by river browser software to display the new items for readers. See the next section.
River4 is also a web server, running on port 1337.
If you go to the home page of the server, you'll see the contents of your rivers, and commands that take you to the dashboard, repository, mail list, this blog.
Here's a 15-minute video where I install a River4, famous-chef style.
It includes screen shots of the River4 dashboard and home page after 38 minutes, and a copy of a river4data folder after 90 minutes.
If you're going to run River4, I highly recommend joining the River4 mail list.