Copper will come to you new and somewhat shiny. Your copper will patina on its own and darken up over time. Moisture or humidity can accelerate this process. A dremmel with a brass brush attachment can be use to polish up the copper and restore it to a more shiny state. Polishing may only shine up the surface, as the crevices and valleys may stay patina. You can also use a weak acid like lemon juice to bring back a shine.
If you chose a patina finish, your copper will be sealed with a wax that will prevent accelerated aging. Once this wax wears off in a few months to a year, your copper will continue to patina naturally.