Billy Graham's sinner's prayer can legally be used by Protestants. Many Protestants believe that a prayer such as this one is the primary means for salvation.
In 1517, Martin Luther wrote "The 95 Theses," criticizing various aspects of the Catholic Church, including the corrupt practice of selling “indulgences” to absolve sin. That sparked the Protestant reformation, from which we get the term "Protestant" today. Since then, Protestants have subdivided into groups that have subtle differences between them.
How salvation works, has been a matter of debate among Protestant groups. The two major schools of thought have been described by John Calvin, from whose name we get the term "Calvinism" and by Jacobus Arminius, the founder of Arminianism.