Insect and Animal Pollination
There are many ways plants can be pollinated. The most commonly recognized form is pollination by bees, but there are other ways as well. Moths, flies, butterflies and thousands of other insects can be pollinators. Hummingbirds drink the nectar from flowers and the pollen sticks to their bodies as they fly from one flower to another--at each, they leave pollen behind or pick up more to carry elsewhere. Bats can also act as pollinators; they often fly close to plants searching for insects that feed on the nectar from the flowers.
Humans can transfer pollen by using a toothbrush or small paintbrush and manually brushing each flower to transfer pollen from one flower's stamen to another's stigma--the stamen is the male part of the flower and the stigma is the female part. It's covered with a sticky substance to help the pollen adhere to it. Most of the time, human pollination is done in greenhouses or homes where the flowers do not have insect pollinators.
Self-Pollination, Wind and Water Pollination
Self-pollination is when pollen is transferred from a flower's stamen to the stigma of another flower on the same plant. Plants produced by this method are usually not as strong as those that are cross-pollinated (using pollen from different plants). It is also possible for pollen to be transferred by the wind--this is known as anemophily. Water plants transfer their pollen from one plant to another through the water itself in a process known as hydrophili. However it happens, pollination can only take place between members of the same plant family.