The Oxygen Cycle begins with plants! They go through a process called Photosynthesis, where they collect energy and eventually create and release oxygen.
The oxygen from the plants is then released into the open air!
HOW DID WE GET UP HERE?
All that oxygen in the air allows us living things to breathe. We exhale carbon dioxide, and the plants take that as energy to produce even more oxygen to repeat the cycle. Go ahead buddy, breathe all you like.