There are 100 years in a century; when used to denote time periods, a century starts with year 1 and ends with year 100. For example, the 21st century describes the period of time from 2001 to 2100.
The word century also refers to a group of 100 similar items. A century was a sub-unit of the Roman army that contained 100 soldiers. Races referred to as centuries contain 100 units (such as 100 yards).
Century was first used in the year 1533. It comes from the Latin word "centuria" and is always used as a noun. A sentence that uses century is "It took less than a century to complete the structure."