First, install Fossil. A current version is here - for Windows, Mac OS/X and Linux (glibc 2.7). My vim installer also includes a recent Windows version of Fossil. Or you can go to the official Fossil website for more information.
Next, ask Ron for a user account here. Remember your username and password!
fossil clone http://email@example.com/p/reva reva.fossil
NOTE: If you decide you want to get the Reva repository, but you won't need to "push" changes to it, you can do an anonymous clone by substituting "anonymous" for "username" above, and simply pressing the ENTER key when prompted for a password. This will give you a "pull only" repository. If you get a username and password later on, you can use "fossil remote" to tell fossil about it.
Fossil will ask for your password, and will proceed to pull the repository. At this point, you have cloned the Reva repository locally. Now, make a directory where you want to put the sources. For example, 'reva'. Change to that directory, then:
fossil open ~/reva.fossil fossil set autosync pullonly
Assuming "~/reva.fossil" is the place you put the 'reva.fossil' you originally created using 'clone', this command will put all the sources in your current directory ('reva', above).
You can periodically do fossil pull; fossil update to bring down any changes to the Reva repository (including Wiki pages and bug reports!). You can also make changes locally using fossil commit -m 'my comment'. If you are sure your changes are "ok", you can then share them with the main repository: fossil sync. Please try to make sure your changes are good before you commit them!