You usually see woodpeckers hanging onto the side of a tree. Many woodpeckers have a black back with white sideways marks. Some have red heads or yellow chests. To find them, listen for their pecking sound.
Woodpeckers have special feet.
Most tree birds have 3 toes going forward, and 1 going back. Woodpeckers are different, because 2 toes go forward and 2 go back. It's like having an extra thumb to help them hold on. Their sharp claws help too. Even their tail feathers help.