An action sampler is basically a cheap plastic camera, with four lenses. When you take a photo, each shutter opens for quarter of a second, one after the other. You can use normal camera film, and get it developed at your normal developers. Each photo you get back will be divided into four, with 4 slightly out-of-sync pictures.
Results aren't outstanding, due to the cheap lenses and construction of the camera (although I think more recent versions are a bit better). The camera doesn't have a flash, so you're pretty much restricted to outdoors photography. And because the lenses are so small not much light gets in. As a result, you'll get best results on a sunny or clear day, not so good if it's a bit overcast.
I've only used mine once, wasn't impressed with the photos, and haven't finished off a second film yet. You might have more luck….
Although it's sold and marketed by Lomo.com, don't confuse it with a Lomo. That is made by a Russian optical manufacturer, and is certainly better quality. The Action Sampler is (or was) a toy camera made in China.
If anyone has any interesting pictures they've taken with an Action Sampler, I'd be interested to put them up on my site, as this section is currently a bit sparse compared to the rest of my site. Get in touch if you'd be keen on doing this