The main tool you will need is a sander but make sure that it is one that you can easily handle. Some people like to use an orbital sander, which is small enough to be hand-held and operates by a cord or battery pack. If you are unsure which to get talk to someone in the home improvement store for their advice. You will also need a shop vacuum cleaner, sandpaper, broom, and hammer. You will also need a stain for the floor and rollers or brushes to apply it along with a sealant. The sealant can be applied with a roller. To avoid inhaling in the dust from the sanding and the fumes from the stain and sealant you should use a face mask.
Make sure that if you have a ceiling fan that you turn it off and close all the air vents. To help prevent the spread of the dust from the sanding you could hang something over the entrance to the room. Since most of the work will be done on your knees you could also invest in a pair of kneepads. Once you have everything that you need it is time to start your hardwood floor refinishing project. When doing hardwood floor refinishing always start in the farthest corner and work backwards toward the door. The first thing to do is sand off the stain on the floor, which is what the sander is for. If you have any stubborn spots you can use sandpaper. After the sanding is done sweep the floor and finish it up using the shop vacuum. The floors have to be free of residue before you can stain the floor.
Make sure that you stir the stain before applying it to the floor to remove any bubbles that could cause a molted look. Use a brush to apply the stain slowly in the direction of the grain of wood. After it dries you will need to seal the floors by using the roller to apply a thin, uniform layer of sealant again in the direction of the grain of the wood. Before moving anything back make sure it is completely dry.