The carbon cycle recycles carbon throughout the world and its' environments. Carbon can not be destroyed or created.
Carbon cycles from the atmosphere to plants during photosynthesis. Then carbon dioxide is pulled from the air by plants for energy.
When I eat the plants, the carbon transfers to me. When I die, I will begin to decay. This process can cause this carbon to enter into the ground. Eventually, the carbon will be turned into fossil fuels.
Whenever animals and humans exhale, they release carbon dioxide into the atmosphere.
Remember the fossil fuels we were talking about before? Fossil fuels are used to power cars, among other things. The vehicle's emissions are then released into the atmosphere when this energy is used.
Once carbon is released back into the atmosphere, the carbon can either move to plants or the ocean. And from there on, the carbon just keeps cycling throughout the earth!