Seeds are made when pollen from one plant lands on an egg in another plant.

In some plants, the eggs are in flowers. The plant makes a sweet water called nectar to get bees, hummingbirds, bats, or other animals to visit. The animals visit several flowers, so they bring the pollen from one plant to the eggs of the next one.

Other plants have no flowers. The wind blows the pollen onto cones or other places.

Why do you think seeds would not be formed underground in roots?

If you are interested in questions like these, you may want to study botany or ecology.

Ferns and mosses do not make seeds. Gymnosperms (pines and their ilk) have cones and the seeds are inside of the cones. Flowering plants produce fruits, with the seeds inside of the fruit.

Seeds are what flowers become after being pollinated by another plant. Reproduction in plants generally requires pollen (small "male" genes) that are transferred by wind or animal to a flower or cone ("female" part). When these two parts come together they form a baby plant (seed). This seed develops a hard protective coating so that it can move away from the parent plant and grow somewhere else. There are many different ways in which plants are pollinated and seeds are dispersed. I highly suggest checking out youtube videos of pollination and seed dispersal. There are some good ones out there!