What goes on in our brain when playing instruments (and other similar activities)?

From my understanding, our brains have every word we know, and when we read it it proscess it faster than you can notice because we are fluent in the languige. If you try to learn a new languige, or a new instrument you normally hesitate more often on proscessing things. But in tasks like reading the human mind works at incredible speeds. Its amazing what our minds can do :)