There are 2 answers to your question, first is the easy answer, and second is a little more complicated.
Answer 1)
Mix sugar, yeast, and water in a gallon jug and poke a hole in the top. shake twice a day and your good to go.
or
Answer 2)
The amount of co2 you disperse will greatly depend on how big the plants are. Therefore, the amount of co2 needed will constantly change. To constantly monitor the co2 levels you will need a co2 montior/controller.
The average co2 level is about 300ppm, or 500ppm if you live in a large city. However, marijuana prefers a co2 level of 1500ppm. Therefore, you also need to decide how you will empliment extra co2. There are many ways to do this. Water + sugar + yeast / co2 generator / Talk to your plants all day / light a bunch of candles / etc etc.
Its also important to remeber that most grow areas are ventilated. So if you have an exhasut fan you will need to consider a constant co2 feed scenario.
Good luck, send a link to your journal when you start one.