P0420 Error Code

I own a 99 Jeep Grand Cherokee laredo and just recently the Check engine light came on, when i checked the code using the on-off method the code displayed was P0420, after looking it up on the net the code has something to do with the catalytic converter effeciency below required level.

Can someone help me out on what possible steps i can take to fix the problem and offer me some insight into what actually in laymans term the problem is.

Thanks.