In one sentence, describe what the following article is about:

The pine flooring should be completely clean of all dust, dirt, and small rocks. Depending on the size of your flooring, run a damp mop or a rag over the surface of the floor. Make sure to clean in the corners of the room and remove dust from any nooks or crannies. If your floor has just been installed, it won't be covered in outside dirt. Instead, you'll need to mop off leftover sawdust from the installation process. Your pine flooring will have many nails driven into each of the wooden planks. Use one corner of the putty knife to scoop a fingernail-sized dollop of putty out of the jar. Apply the putty into the countersunk nail hole, and use the flat edge of the putty knife to smooth the hole flush with the flooring. The filled holes will level the floor and provide a uniform stained finish. You can purchase both a putty knife and the hardening putty at a local hardware store. If the store offers different colors of hardening putty, select the color that most closely matches your floor. Wait until the putty is fully dry before you begin to sand and finish the flooring. Gently press on the filled countersunk nail holes to make sure that the putty is firm. Whether your flooring is freshly installed or has been in place for years, it's bound to have minor scuffs, marks, and scratches on it. Clear these unwanted marks by sanding the entire floor. Sand on your hands and knees using broad, straight strokes. Sand along the lines of the wood grain. Coarse 120-grit sandpaper will remove unwanted marks without adding scratches to the pine wood. If you're sanding a large area of flooring and prefer not to sand on your hands and knees, you can rent a sanding machine from a local hardware store. To protect your lungs from the sawdust produced by sanding, wear a bandana or protective face mask over your mouth. After you've sanded the floor, it will be covered with tiny pieces of wood dust. Remove these by dampening your mop and running it over the floor. Alternately, you could dampen a clean, lint-free rag and use it to clean up the floor.

Summary:
Clean all dust and debris from the floor. Fill countersunk nail holes with hardening putty. Give the putty 3 or 4 hours to dry. Sand the pine flooring with 120-grit sandpaper. Clean the floor with a damp rag or mop after sanding.