They agreed to start negotiations on a new accord that would place all countries under the same international requirements with respect to controlling the emission of greenhouse gases, which would take effect, at the latest, by 2020. This is a historical deal like the Kyoto treaty; however, the participants in this deal would be more expansive, especially if the US, China and India follow their commitments here.
In addition, to the agreement on greenhouse gas emissions, the parties agreed to set up bodies that will collect, govern and distribute tens of billions of dollars a year for poor countries. This is very important because many of the countries that will be hit hardest economically by climate change are the poor countries and, more importantly, the poor countries need additional funding to advance their technology to more green/carbon neutral type of products.
Also, the agreement sets out rules for monitoring and verifying emission reductions, protecting forests and transferring clean technologies to developing countries.
This is a good start, with the emphasis "start". They key will be all the parties to this agreement following through. More importantly, following through sooner than later. Unfortunately, the Earth's climate is already changing. Depending how quickly we act, we may be able to slow down this process of change where the concept of a white Christmas in the Northeast of the United States does become something of folklore and myths, like that red nosed reindeer.