There are many different types of marble out there, and they all seal differently. For some, you can use a regular polyurethane aftercare sealant that will last 2–3 years before re-application, while other marbles require special types of sealing.
If your stone is not sealed then look under it to discover its makeup. If it is pure white with veining that looks like snaking rivers running through it, or a solid black slab; then go ahead and choose whichever method you prefer to seal your floors. But if your floor has blue/green veining throughout in addition to the white veins, or it has pink or red tones in it, then you will need to choose a sealant that is made for sealing marble with dark veining.