Composed of over 1013 neurons, the human brain has been said to have more synapses than stars in the universe. How do you begin to understand all the madness compressed into the three pound ball of flesh? I have no idea, and I don't trust anyone who claims to know either. However, there are some clever approaches to chipping away at the problem.
At the systems-level, the brain distributes computation over multiple regions. A good analogy is a peer-to-peer network that distributes number crunching across multiple computers, where each computer is specialized to perform some specific aspect of the computation. Abstract this by simply calling the computers "nodes" (which can represent anything, for example, brain regions) and the connections "edges," and viola! you have reached the entry point of network theory, which is a quantitative and visual approach to understanding how nodes relate to one another and how networks function as a whole.