Obamacarea s tax credits: Tell me again how they work?

About 6 million of the 7 million people expected to buy health coverage on the new insurance marketplaces next year will be low- and middle-income consumers who'll receive federal subsidies, or "tax credits," that will drastically cut their costs, according to the nonpartisan Congressional Budget Office.

http://www.star-telegram.com/2013/09/24/5190364/obamacares-tax-credits-tell-me.html