The bird's bill is a remarkably useful instrument that comes in all shapes and sizes. The bill shows various adaptations for methods of feeding.
Birds with all-purpose bills have general sort of diet using a bill that can cut, crush, rip, and open just about anything.
Some other examples are short thin bills for insect eaters, short thick bills for seed eaters, long thin bills can be for probing flowers for nectar or probing soft mud for worms and shellfish, strong hooked bills for tearing meat.
The huge bills of Toucans are both decorative and functional. Being light, as well as long they allow the birds to pick fruit from the thin ends of branches that can not support the birds weight.
Flamingos are filter feeders, and have many complex rows of horny plates that line their bills to strain food items from the water.
Of course, gathering food is not the only use for the bird's bills. Birds use their bills in fighting and in defense of their territory, gathering nesting materials, building nests, grooming feathers, attracting mates, scaring predators, and other important rolls.