They use what is called echolocation to find their food. Because they hunt at night when it is dark, they cannot see their prey. So, they make clicking and squeaking sounds and listen for the echo to come back to them. If the sound comes back quickly, they know something to eat is nearby. If they hear no sound, they know nothing to eat is close.
Most bats have big ears and very good hearing.
A few species of bats eat the blood from the backs of cattle and the feet of chickens. These vampire bats slit the animals skin with their sharp toenails, and then lap up the blood. The bloodsucking bats of the movies are not real. The largest bats have a wingspan of more than six feet. However, most are smaller.