While people have toes on the end of their feet and cats and dogs have paws with claws, animals like cows and horses have hooves. A hoof is just the tip of the animal's toe, encased in a hard substance made out of the same stuff as our fingernails are made from. Hooves continue to grow just like our fingernails, and are worn down by the animal walking around. If the animal like a horse walks around on very hard ground like a road their hoof will wear down too fast, so people make them special shoes to protect their hooves. The hoof in the picture is a cow's hoof. Cows have cloven feet, meaning the hoof is divided into two sections.
A roof is the topmost part of a house or building. Rooves are usually sloped and watertight so rain and snow runs off them and doesn't go inside the house.
Something is waterproof if water cannot pass through it or soak into it. The raincoat in the picture is waterproof.