Hello Littlewing I'll try and keep it really simple .....................
A plant is programmed to flower at a certain time of year. It will grow during the Summer months and when Summer starts to end it will flower, It knows when to start flowering due to the hours of day light getting less.

When growing indoors we trick the plant in to starting to flower by reducing the amount of light we give it...............usually by reducing the light to 12 hours a day.

There are a few varieties that will start flowering with more than 12 hours light but in general most will respond to the 12/12 flowering cycle


There's lots on these boards about flowering, I've just written the absolute basics


love mand xxx