How does a bird catch its food?

This depends upon the type of bird you are asking about. Hummingbirds feed on the nectar of certain flowers, so they "catch" their food by flying up to it. Turkeys feed on grains and insects, so they catch their food by grazing/foraging along the ground. Falcons feed on other smaller birds as well as smaller mammals, reptiles and fish (depending upon the environment and the species of falcon), so they catch their food by gliding on the thermals and then diving/stooping on their prey. Penguins feed on fish in the ocean, so they catch their prey by swimming through the water and catching the fish on a turn, dive or uprising. Buzzards feed on carrion, so they "catch" their prey simply by gliding down to a carcass and eating.