They have a nice interactive Flash demo which explains what PCR is and how to use the machine: http://openpcr.org/use-it/.
There ought to be some explainer on the home page. I was staring at the page thinking "...okay, and this thing is ???" The less curious will just leave. Perhaps you want that?
It can do a lot more than that, but yeah that's definitely the first/primary job of a PCR machine.