Terraforming? How is it done?

Can anyone tell me how terraforming (i dont know if thats how you spell it) is done because i know people want to do it to mars and i know what it does but i just want to know how you actually do it? thanks :D with mars it is theoretically possible to terraform it, but it would take a very long time and we would pretty much be doing it blind b/c we have never done it before in real life. any way, first u find a suitable planet that is in thew goldilocks zone (zone where life can occur on a planet with liquid water; Earth is in the goldilocks zone), then start pumping CO2 into the atmosphere. once the atmosphere is thick enough, we would put genetically engineered plants there that would start converting the CO2 to oxygen. after the planet developes an atmosphere similar to that of earth, it will become inhabitable for humans.

The whole process would take several hundred years. and keep in mind that this is only in theory