You can polish rocks by hand or by mechanical means. For bigger rocks use progressively finer wet sandpaper to get to that luster. If you have a large craft or hobby store near you they will carry small rock tumblers that will polish all your rocks. You can find more info at: rocktumblingsupplies.com
There are several ways to polish rocks. Some people polish them by hand, but it's more convenient to use a rock tumbler. You will also need a non-abrasive soap bar, abrasive grit, plastic pellets and a few other things.
To polish rocks you can use a rock tumbler for the ultimate smooth shiny rock. If you don't have a tumbler you can use a dremel tool or buffer but it won't be the same.