It means take one tablet by mouth twice a day. Since a day is 24  hours, dividing that by two means one tablet every 12 hours.
The nicotine patch is an over-the-counter medicine that can help people stop smoking. The nicotine patch (NicodermÂ® CQÂ®) is a nonprescription medication used for nicotine replacement therapy. It helps people stop smoking by reducing nicotine withdrawal symptoms, including nicotine craving. Nicotine is a highly addictive drug. Each time you inhale from a cigarette, nicotine rapidly enters the brain, reaching peak levels within 10 seconds. In the brain, it activates brain reward centers, leading to feelings of pleasure. The effects of nicotine disappear quickly, however.
Nicotine chewing gum and transdermal patch are both effective aids for nicotine dependent smokers who seek help in giving up. In the most highly nicotine dependent smokers (craving a cigarette on waking) nicotine 4 mg gum seems the most effective form of replacement therapy at present.