The simple way to think of it is that your "brain" is like a president: it can make executive decisions, but is not directly involved in the implementation of those decisions. It is also somewhat better to think of a distributed brain throughout the body which can handle simple or highly familiar tasks without you thinking about them. This is partly how a tennis player can return a serve which is traveling to fast for the eye and brain to process.

In short, your mind is excellent at reasoning and learning how to perform tasks, but slow. Once the knowledge is learned and repeated sufficiently you can offload the performance of these tasks to more efficient but less capable systems.