Alright, I'll do my best to explain it. Basically, Cap & Trade is a system by which companies are supposed to reduce carbon emissions. It's been tried before on a smaller scale with sulfur dioxide emissions to reduce the occurance of acid rain (which did work, but as I said, on a smaller scale). Cap & Trade functions by giving certain tradeable commodities to companies that reduce their carbon emissions, thus incentivizing the process by which they reduce them. These credits can be traded to companies with emissions above the cap to help them avoid tax issues. The disincentive comes through companies that retain high carbon emissions, since they will be taxed according to the excess. It's enacted over a long period of time, whereby the amount of emissions is gradually reduced to ensure that companies are able to keep up. In the cases of sulfur dioxide, this worked well because companies eventually started going well below the cap in order to gain more of these credits. It's uncertain when it comes to carbon because it is such a staple emission, practically every company emits some carbon, and it's difficult to shift away.
Hope that suffices.