Basically, in a supplemental draft, to draft a player in each round, you give your pick in the same round in next year's main draft. So, if the Chargers select Mike Williams in the first round, they lose their first round pick next year. As an example, the Texans selected RB Tony Hollings in last year's supplemental draft in the second round, and they lost a second-rounder this year.
The only really famous player to be picked in one was Bernie Kosar by the Browns.
Here's another explanation...
http://www.profootballweekly.com/PFW...ge=21667&post=