Other contributors have said "How is a flower is pollinated by insects?" is the same question as "How is a flower pollinated by insects?" If you believe that these are not asking the same thing and should be answered differently, click here
Usually pollination occurs from bees. They will land on flowers and some of the pollen will stick to their legs. When they go to another flower, some of the pollen drops off of the bees legs. That is how pollination occurs.
The answer is really pretty simple. Flowers that are pollinated by insects are pollinated by insects going from one flower to an other. Carrying pollen from one flower to the next. Wind pollination...