How and when to use co2 tanks

I am in need of help with how to use co2 and when to introduce it to your plants. I have no clue and your help would be appreciated.

Basically, I am looking for an A-Z on co2 tanks.

Thank you in advance!

u can use co2 anytime the lights are on in veg or flower it just increases the growth but most ppl just use it in flowering to beef the buds up