wait for it to mature than when its about to send its pollen out you put a bag over it and shake it alot, this will knock all the pollen off the plant into the bag where you can keep it by freezing it. then when you want to pollinate a female you take a brush and dip the brush it the pollen and sort of paint the pollen onto the females bud sights. usually when people pollinate is because they want to get seeds or some people say if you only pollinate on side branch of a female the rest of the plant produces more THC making it more potent bud and then you will have some seeds also but just from that side branch.