If you don't know then it is almost certain that you ARE growing photo-period plants. The alternative is Auto-flowering plants, but you would have to order special seeds for those.
The photo-period plants require a dark period to be flipped into flowering. Most growers use a 12 hour dark period for the duration of the flowering period of the plant. During those 12 hours it must be totally and completely dark. Any light at all, even an LED indicator light on a powerstrip, will prevent the plant from flowering.