A seed needs a suitable place to grow. If every seed landed directly beneath its parent plant, many young plants would compete for space and light. Seeds can reach new places in several ways.
Some seeds travel in the wind. A dandelion seed has a light, feathery structure that can help it float through the air. It does not choose where it lands. A breeze may carry it to soil, but it may also leave it on a pavement where it cannot grow.
Other seeds travel with animals. A hooked burr can catch on fur and be carried away. Later, it may fall off in another place. Some fruits contain seeds that animals eat along with the fruit. Those seeds may be left elsewhere after passing through the animal.
Travelling is only the first part of the process. A seed still needs the right conditions to begin growing. Reaching a new place does not guarantee that it will become a plant. The journey gives it a chance.