There are 24 Essential Vitamins and Minerals, twelve of each.
These compounds are normally obtained through a healthy diet, and are absolutely crucial to intake (via either supplementation or diet) for optimal human functioning.
Ingesting optimal levels results in optimal human functioning (relative to deficiency states), having a lesser than optimal intake results in what are known as 'sub-clinical' deficiencies which are non-optimal states that are not necessarily adverse.
Although rare, clinical or 'true' deficiency states may occur with prolonged avoidance of said vitamin or mineral. These states usually have unique names, like Rickets (Vitamin D deficiency) or Scurvy (Vitamin C deficiency).
Higher levels of vitamins and minerals, above what is needed for optimal health, is not necessarily better and may actually be harmful. Each vitamin or mineral has a recommended intake range which should be aimed for through diet first and supplementation afterwards.