There are three requirements for becoming a saint of the Catholic Church. First, a bishop investigates the candidate's life to make sure she is worthy of sainthood. Second, the church official collects testimonies and documents, analyzing them for instances of virtue, distinction, bravery and/or martyrdom that set the candidate apart from her peers. Third, the candidate has to have performed at least one miracle. The pope has the final say on whether or not the candidate achieves sainthood.
The church grants the candidate a new title for each requirement achieved: "Servant of God" for the first, "Venerable" for the second, "Blessed" for the third and finally "Saint" with the pope's approval.
Technically, a person must be dead for at least five years before being considered for sainthood. However, that is not always the case. For example, Mother Teresa was dead for less than two years before the church began the process under Pope John Paul II. Also, the church usually requires more than one miracle but often waives that rule as well.
The church official that collects the documents and testimonies is called a postulator. He is in charge of advocating for the potential saint and coordinating the whole process.