Hi Nancy, Here you go..... a diamond bit is the key to success! Available at any home improvement or hardware store.
The diamond bit is the way to go but I would also recommend that you place a piece of tape where you are drilling to help to keep the area solid while drilling so that it does not break away.
Put a piece of duct tape on the bottom, start with a small drill bit, go bigger if necessary. For planter drill 3/5 holes depending on size