What does the word "dispersal" mean? Dispersal means scattering or distribution of something.What is a fruit? Fruit is the part of the plant that protects seeds as they grow. Fruits can be fleshy and juicy—like apples and oranges—or dry like nuts or peas.
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People plant some seeds, but most plants don't rely on people. Plants rely on animals and wind and water to help scatter their seeds.
Animal dispersal
Animals disperse seeds in several ways. First, some plants, like the burr at left, have barbs or other structures that get tangled in animal fur or feathers, and are then carried to new sites. Other plants produce their seeds inside fleshy fruits that then get eaten be an animal. The fruit is digested by the animal, but the seeds pass through the digestive tract, and are dropped in other locations. Some animals bury seeds, like squirrels with acorns, to save for later, but may not return to get the seed. It can grow into a new plant.
Wind dispersal
The kind of seeds which are often wind dispersed are smaller seeds that have wings or other hair-like or feather-like structures. Plants that produce wind blown seeds, like dandelions, often produce lots of seeds to ensure that some of the seeds are blown to areas where the seeds can germinate.
Floating in water
Many aquatic plants and plants that live near water have seeds that can float, and are carried by water. Plants living along streams and rivers have seeds that float downstream, and therefore become germinate at new sites. The size of the seed is not a factor in determining whether or not a seed can float. Some very large seeds, like coconuts, can float. Some small seeds also float.
And some plants disperse their seeds in other ways...
Some plants have unique ways to disperse their seeds. Several kinds of plants "shoot" seeds out of pods. The seeds can travel quite a few feet from the plant this way.
Check out this video from the Missouri Botanical Garden about different ways seeds are dispersed:
Animals disperse seeds in several ways. First, some plants, like the burr at left, have barbs or other structures that get tangled in animal fur or feathers, and are then carried to new sites. Other plants produce their seeds inside fleshy fruits that then get eaten be an animal. 
The fruit is digested by the animal, but the seeds pass through the digestive tract, and are dropped in other locations. Some animals bury seeds, like squirrels with acorns, to save for later, but may not return to get the seed. It can grow into a new plant.
Many aquatic plants and plants that live near water have seeds that can float, and are carried by water. Plants living along streams and rivers have seeds that float downstream, and therefore become germinate at new sites. The size of the seed is not a factor in determining whether or not a seed can float. Some very large seeds, like coconuts, can float. Some small seeds also float.
