Only a few specific strains will flower by themselves. Lowryder is one. Ruderalis is what i believe the family to be.
Most will need to be put onto a 12 hr dark period before flowering and blooming. In the outdoors, this would mean days were getting shorter and it was time to flower and repopulate.
You start a seed..
Transplant to you medium (soil, hydro)
You leave the plant on 18 hours light 6 dark. When the plant reaches the desired height, you switch to 12/12 , keeping in mind that a week after you change the light the plant will "flower". when this happens it will double to triple in height in about 2-3 weeks. Then the plant produces flowers and building up "buds" you want from the time of the 12/12 light switch to last for 8-12 weeks before you harvest the plant. If you are working in soil, the seasons dictate when your plant will be in vegitative growth, or flowering.