Engineer Graham Stoney tries in a single article to explain how the brain works.

It's a compelling read:

Given that our brain is where the thoughts, feelings, ideas, beliefs and decisions that guide our whole life arise I think it’s helpful to have a rudimentary understanding of how it works so we can use it more effectively.

Your brain is the most complex system in the known universe. Over eighty billion massively interconnected neurons form the most complex parallel-processing biological computer imaginable, and it’s right there in your head controlling your every move. Nobody fully understands how it works, which isn’t at all surprising when you consider that we’re using our brain to try to understand itself. That’s like a computer trying to understanding itself...

Topics he covers include Consciousness, Pattern Matching, Emotions, Thoughts, Fear, Mind and Body, Memory, Learning, why Repetition Feels Good, Empathy, the Need to Socialize, Social Grouping and Prejudice, Projection, Creativity, and Limitations.

As I said, it's a compelling read.

This is related to flow. bakadesuyo says:

Flow is the mental state of operation in which a person in an activity is fully immersed in a feeling of energized focus, full involvement, and success in the process of the activity. Proposed by Mihály Csíkszentmihályi, the positive psychology concept has been widely referenced across a variety of fields.

The likelihood of experiencing flow is positively related to novelty seeking, persistence, and self-transcendence, but negatively related to self-directedness.

Flow is the brain operating at full capacity.