The US agreed to reduce its average emissions 7% from their 1990 levels during the period 2008-2012.  Other developed countries agreed to similar reductions.  The way the reductions were achieved was up to the individual countries. Developing countries did not agree to meet any requirements.
It incorporated some novel mechanisms for achieving greenhouse gas reductions, including emissions trading, and joint implementation.  These flexible, market-based mechanisms were included with the urging of the US delegation.