Your brain is the most important organ in your body. It controls all of your other organs subconsciously while controlling your movement consciously. This means that your brain makes sure that your heart beats and your lungs breathe without you having to think about it (subconsciously). It also means that when you want to move (consciously), your brain makes sure that the correct muscles work to allow you to move.
Here is an example of how your brain works.
If you decide you are going to walk, a part of your brain is activated by your
thought. This part of your brain co-ordinates the activity and sends information
to all of the correct areas of your brain that are involved in controlling walking.
The correct muscles have to be told to move. Other muscles have to be told to
relax. Parts of your body have to be notified so that you can have appropriate
balance while you are walking. Other parts of your body have to be notified
so that your heart rate changes and your breathing rate changes in order to
efficiently supply your body with the proper blood and oxygen. There are also
many more things that have to be notified so that the activity of walking can
occur. Your brain then sends the information down your spinal cord and out your
nerves to the places in your body that need to work.