Questions about ventalation and co2 levels and how to keep them???

hi i have a small growing area its 4x4x7ft tall ,, the question or problem im having is i wanna add co2 to this area but since im new to this im not sure on how to do it properly ,,, how should i vent it correctly? so i dont waste the co2? i have a hole where i can put a fan that would have fresh air from the out side avaliable?? do i want the fan to suck the air out or do i wanna blow fresh air in?,, the grow room is indoors but has a wall that had some sort of vent hole prevesiouly so i can get fresh air from out side if needed?the hole is about a 6 inch hole .. anyway,, im not sure on how the venting should go fresh air in or suck old air out?and when should i add co2? the plant i have in their is starting to flower????and how do i run my system correctly with out a logic controll ?? im only have timers so every thing has to be in the right order???? pls help if u can????

im still looking for help on this matter im not understanding how to vent my room properly and still keep co2 lvls ambient?

here you go


How to control the amount of CO2 in the growing area

are u looking to use tank co2? if so you dont need to vent at all, and u only need to run co2 during lights on..
Seeing as u already have vent holes cut and u dont mind cutting holes etc just have an air intake vent and exhaust fan, just make sure the passive intake vent is twice the size of the exhaust fan