Calcium is the 20th element on the periodic table. It is also the 3rd alkaline earth metal of the periodic table.
Calcium metal itself is rather reactive. When reacting in water, it vigorously reacts to form calcium hydroxide.
Calcium metal itself isn't used often, as it is difficult to store and that it is really reactive. However, compounds of calcium such as calcium salts are commonly used in the laboratory. Also, calcium in the form of calcium phosphate is found inside bones and teeth.