How do birds' build their nests?
All depends on the bird. A lot of birds build their nests with branches, leaves, feathers, and occasionally pieces of trash lying around. Most use sticks for the structure and the use feathers and leaves for bedding. When I said trash, I meant pieces of strong yarn, anything soft.
Birds build their nests in different places depending on their habitat. Most build them up in the air, in trees, sides of cliffs and buildings. This allows them to be protected from most of the predators that can't fly or climb. There are flightless birds and many water fowl that build their nests on the ground.