There is a thing called a toothbrush and toothpaste also exists. be patient and use those enough and your teeth will be white.
That doesn't always work. My teeth had ridges on them, so even though I brush my teeth twice a day everyday, my teeth were never as nice as I wanted them to be. I forgot to mention that to get rid of those ridges, the dentist (without permission, she's scary) used a sander and fixed my teeth so that the ridges were gone. After that, my teeth became so much nicer, especially with a little help from teeth whiteners. Now my teeth are really white. Well, really white in a natural way.
Yo. I know it doesn´t works always but it actually works for me atleast.