Tax Sale Certificates for Houses..How do they work?

Hello all. I came across some information for my county on tax sale certificates, but I was wondering if anyone here could shed some light on how they work or why they’re beneficial to real estate investors. Any information on that subject would be greatly appreciated. I looked at the site and many homes were “sold” that way. They even offer an exclusive service for investors that gives you info before it hits the newspapers etc. So I want to know if it’s worth it. Thanks.

Shania