Your teeth can become discolored due to various factors. Things like coffee, tea, and red wine can stain your teeth. Smoking can also discolor your teeth. Not brushing and flossing leads to staining too.
Teeth whitening kits use special chemicals to break up these stains. This makes your teeth look lighter and brighter. The whitening products only help with surface stains. Though, they may not work well on deep stains inside your teeth.