To describe a zoo, you might begin by outlining its size and layout. For example, you could mention the number of animals it houses, the variety of species it exhibits, and the size of the grounds or enclosures. You could also describe the physical setting of the zoo, such as its location (e.g. in a city, in a park, etc.), the layout of its exhibits, and any notable features or landmarks (such as a large aviary or a reptile house).
Next, you might describe the types of animals that can be found at the zoo. This might include a list of the various species or a general overview of the range of animals on display. You could also mention any notable or popular attractions, such as a famous gorilla exhibit or a penguin habitat.