Since pollen can't walk, insects moving from one flower to another carry the pollen grains so a new fruit can be formed. Some pollen can be blown by the wind from flower to flower. Windborne pollen in the air is what causes allergies in people who are sensitive. The honeybee actually visits flowers to get food. Bees collect the pollen from flowers and take it back to the hive where it is stored until it is used to feed the bees in the hive.
Bees also get nectar from the flowers they visit.
Nectar is produced by plants, and is a sugar filled liquid that bees drink from the flower and carry back to the hive where it is made into honey. As the bee moves from flower to flower getting food, the plant benefits in being able to produce fruits, with seeds that can grow into new plants. Plants and their pollinators have been benefitting each other for over 100 million years. The are lots of pollination experts on the web. You can read about Pollination of citrus fruits , or check out this great article and lesson on all sorts of pollinators.