The role that owls plays in food chains is generally that of consumers, and they are often apex predators. Owls eat other animals, but few to no animals, depending on the food chain, eat mature owls.
A food chain or food web consists of different trophic levels. A trophic level is a rank in the chain indicating what an animal feeds on. For example, autotrophs such as trees use photosynthesis to feed themselves. Autotrophs exist at the trophic level of producers: they generate the food that other creatures eat.
Animals like mice are consumers. They consume autotrophs. Because they eat autotrophs, they are on the next trophic level up from them and are called primary consumers. Animals, such as snakes, that eat mice, are also consumers, but they are another trophic level above mice because they feed upon them. They are secondary consumers.
Apex predators are creatures that eat other consumers and that have no creatures with a trophic level higher than them on their food chain. Owls are generally considered apex predators, though some owl species may be preyed upon by other owls. Owls are predatory birds, so even those that are not apex predators are still consumers.