Information about RSS
There are several sites out there that explain the whole concept of RSS in general, such as WhatIsRSS.com, but it would probably be simpler if I explained it with almost the exact same text I used to explain it with at WSSQUID:
Currently, in order to find out when new comics have been uploaded, you'd have to keep checking this site every now and then. Which can be time-consuming and even though James usually updates every Monday and Friday, you may forget to check or the comic may be slightly late. The basic concept of RSS is that it can automate this process (and not only for this site, but many others as well, including news sites, blogs, other webcomics, etc) and notify you whenever any of them has been updated.
The most convenient way to use RSS feeds, in my opinion, is via a browser feature or plug-in.
If you are using Opera (version 7.5 or newer), you should be able to subscribe to the RSS feed simply by clicking on the link.
If you are using Mozilla Firefox, you will just have to install an extension and you're good to go.
If you are using Internet Explorer, you can either use a plug-in such as Pluck or an external application such as FeedReader, but personally, I would recommend switching browsers to either of the two mentioned above.
If you haven't tried out either of them, I suggest reading these pages:
Opera Feature Tour
Why use Firefox?
Or for something less formal:
GGC Media :: This is really good, G
Whether to choose Firefox or Opera is a matter of personal taste. As you may have guessed, I prefer the latter.
Most people tend to ditch Opera the minute they find out that it displays ads all the time, but it's not nearly as bad as it sounds. The space it uses up is almost negligible and the text ads aren't very annoying so you'll likely get used to them and won't even notice the ad-bar after a few days of use.
Update! - Actually, Opera has been ad-free for several weeks now, since the release of version 8.5! (Thanks to Tim for reminding me)