Brain is composed of nervouse tissue and informations goes form cell to cell by neurotransmitters and by electrical action potentials. This is common with all brains(including animal brains).
For the humans, there is a specific strcture called the limbic system that regulates our affective life and memory. Theese structures are shared by all humans in an identical way. The way the information is sent and stored differs from person to person.
The brain has different commanding centers = motor center in frontal lobe, sensitive center in parietal lobe, seeing center, etc. (for all different actions there is a commanding center).
Now, for the difference among us in a more astract way. Everybody can study to understand principles, theories and advanced formulas. The difference is made on theoretical mathematics, physics or even theology. Imagination witch respects and bends to a good limit some laws and innovation makes the difference.
Some are not smarter than others, but are not that limited. There are a lot of aspects we do not understand and probably witch we will never understand. We are limited by nature and by our learning reflexes but we also have a rather *personal* limitation.
That limitiation varies from person to person and it can only be pushed further and further away by innovative persons who bend laws and create theoretical formulas witch in the future can be validated by other people.
We all have the same potential, but it is limited by only ourselves and for each person that breaks the barrier limitation, wee all raise the barrier a bit, and a bit, and a bit.... Everyone is influenced by inovations found by the *more unlimited* persons and everybody is influenced by everyone until they are able to rise above the mass when they are developed enough and able to make innovations by themselves, so the next generation can grow even more and more until the end of all, or the *reset* of all.