you don't have to use "synthetic" CO2 to grow, you will do quiet well without any extra CO2 in your grow as i do but you have to make sure that their is a proper air exchange then in your grow since this will be your plants source for "natural" CO2 which it need to grow no CO2 at all, no grow
so if you don't want any extra hassle with synthetic CO2 sources you have to ensure a proper ventilation of the grow as within the grow, so to set up fans in it to move the air around and feed it to your babies
your plants will actually produce their own C=2 during the dark cycle in your grow since they then use up suger and O2, so cut back on ventilation of the grow short befor and after the dark cycle and totally in the dark cycle. you still have to keep the fans within the grow going!!!
it ain't much but just a little extra, so you mid not want to wast it
oh, and if you go for this method, please monitor the humidity in your grow during dark closely to avoid peaks which could lead into fungus infection in your grow! (its just worth case scenario, but shit can happen if you won't watch out)
no, CO2 is a part of the gases mix air consist of... fans will spread it evenly in your grow, do the winds job in it. without that gas movement your plants would use up all CO2/O2 in seconds and then starve because no fresh is delivered to them.
a CO2 drip sys will provide some extra CO2 to your plants, but you will still need a fan to get it moved to them... and the sys itself consist of a bound form of CO2, CaCO3 for example which is split up by a mild acid like vinegar... so stuff you should have heard of in school somewhere between kindergarten and early junior high