Don’t understand how to use Lightbox/Shadowbox

So I’m setting up a blog for the first time. I immediately moved back to WordPress 2.7.1, which I’m using now.

I want to set up a Lightbox/Shadowbox type image viewer, and neither seems to work. I see online that Lightbox doesn’t work in 2.7.x, so I installed Shadowbox. But I can’t seems to get Shadowbox to work either, and it’s documentation on how to use in WordPress doesn’t seem to exist.

I can install the plugin, but how do you use it? I’m having a very tough time troubleshooting, because I’m not even sure how it’s supposed to work. If someone could tell me how to use Shadowbox I would appreciate it.