Every time we learn something of consequence, we change our brains a little bit. Learning involves physical alterations in neurons and in the synapses that link them together. These minute structural changes in individual neurons underlie broader changes in the functional organization of the brain.
Learning induces the formation of new synapses, and this in turn seems to make neurons more efficient or more powerful. Practicing something repeatedly is an effective way to learn something because it involves repeated activation of the same neural pathways, which become stronger and more efficient each time.
Metaphorically, learning could be compared to forging a new path through a thicketed wood. Each time the same path is used, it becomes clearer and more easily navigated. If used enough, the path can become a permanent addition to the landscape. The same principle holds true for neural pathways when we practice something repeatedly, such as when learning a musical instrument.
Over the course of a lifetime, learning and life experiences create a rich network of circuits uniquely fine-tuned to each individual. Learning literally shapes and reshapes the brain in this way.