Ceramic tile floors are great because they can take so much of use. That's why they're so often used for bathrooms, kitchens, and entryways. The glazed surface of the tile is hard, durable, and it rarely stains, but the grout that fills the spaces between the tiles, now, that's another story. Unless you're the tile setter, who laid the floor, used one of the new stain-proof grouts, it's just a matter of time until the stains appear because traditional, sanded grout is very porous, so it soaks in anything that contacts it. If the floor is new, you'll have to wait 30 days or so for the grout to fully cure before you can seal it. If it's older, you wanna clean it well first. A mild bleach solution and a stiff scrub brush should do the trick to remove the dirt and hopefully any stains that are already there. When the floor is completely dry, you're ready for the sealer. All this stuff usually cost about 5 bucks, but while you're shopping spend another 5 or so for an applicator bottle. This one has different-sized wheels for different widths of grout joints. As you roll the bottle over the floor, the wheel spreads the sealer on just the grout line so the process is neat and clean. If you waited too late, and the floor is already stained, you can stain and seal the grout at the same time with one of the new grout stain pens.