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 replacement therapy works best when used in conjunction with a support program, such as counseling, group therapy, or behavioral therapy. Nicotine chewing gum, if chewed correctly, increases quit rates up to 2-fold. At 1 year, the abstinence rate with the patch is 20%. At 4 years, the abstinence rate is 12.4%, as opposed to 4.5% with placebo. Nicotine patches are sold under various trade names (see below).