Properly Applying c02

Hey guys, I have my plants growing in the basement, I moved my plants yesterday into my celler and I found a GE Sunlight. I dont know how many watts it is because it doesnt say, but the person who lived here before me grew and left it behind so I am assuming its a good grow light. I need to know how to properly apply c02 to my plants without any kind of danger to them, I want to get them premo'd up before I harvest :D.

http://www.hydroponics.net/learn/co2_calculator.asp

Try this link.

Does this have to be EXACT? or roughly?