Some fruit trees such as certain types of apple trees are not self fertile. This means that they need to be pollinated in order to grow fruit. Pollination is the process of moving pollen from one flower to another by pollinating animals such as bees, ladybugs, beetles, moths, and hummingbirds. Bees are very important pollinators because they pollinate about 70 types of crop species that help to feed 90% of our population.
If you are looking to attract pollinators to your garden here is a list of plants and the type of pollinators they attract.