1. Canopy: This is the uppermost layer of the forest, consisting of the crowns of mature trees. It provides shade for the lower levels, and is home to many animals like birds, squirrels, and insects.

2. Understory: This level is found beneath the canopy, and is populated by smaller trees, shrubs, and saplings. It receives less sunlight than the canopy, and is inhabited by animals that prefer shade, like deer, rabbits, and snakes.

3. Forest Floor: This is the lowest level of the forest, consisting of the soil, decaying leaves, and other organic matter. It is teeming with invertebrates like earthworms, fungi, and bacteria, and is home to many small mammals and reptiles.

It's important to note that these are just general levels, and the specific structure of a forest can vary depending on the type of forest, the climate, and other factors.