Hummingbirds fly from flower to flower, sticking their beaks
into the center to take sips of nectar. While sipping nectar,
hummingbirds are inadvertently transporting pollen grains from
previously sipped flowers. The process results in the cross
pollination of different flowers, through the help of the
hummingbird.
Basically: Hummingbirds help flowers pollinate each other, which
allows flowers to reproduce.