So... How does this work?

[Chris Bork]

I'm researching investing in tax liens in my county (DeKalb County Illinois). I understand the basic concept, but looking on the county website on the FAQ page I found something confusing. Once a year they hold a delinquent tax sale. They state that all liens will be sold at the auction. How ever they also have a tax deed auction, as well as assignable certificates. So my question is, how does the progression work? If all liens are sold at the auction, how do we end up with assignable certificates, and how does the tax deed auction come into play? I understand the individual components, just not how we get from point A to point B. Or are they totally different functions separate from each other?
If some one could shed some light on this it would be great. Thanks!