How much vitamins do I need?

The answer to this question depends upon your age, health and nutritional status. The question of how much of a vitamin is enough is still debated among scientists and health care professionals.
Initially the FDA published MDA's (minimum daily allowances) for vitamins and minerals. These amounts were needed to avoid diseases seen with specific vitamin deficiencies
In the 1980's this was revised to RDA's (recommended daily allowances). Generally the requirements were increased above the MDA's. RDA's took into account that low levels of certain nutrients, although not low enough to cause a deficiency related disease, might nevertheless interfere with optimal health.
Most recently terminology has again changed to "Percent of Daily Values" or "% DV". This is for an assumed 2000 calorie a day diet. DV's are generally much higher than "minimum requirements".