"A creed is a statement of faith for public use; it contains articles needful for salvation and the theological well-being of the church" (Cairns 177).
The earliest creed is a baptismal creed known as the Apostles' Creed. Nobody know when it developed but people think it started with Peter's confession in Matthew 16: "You are the Christ the Son of the Living God." Those words are the foundation of the church.
Then, when they trained young and new believers in the Faith, they would teach them this Trinitarian creed in order to express faith before being baptized as believers and before baptizing the rest of their household into the Covenant Community.
During the Arian controversy of 313, people developed the Nicene Creed for a more specific description of the three members of the godhead. Throughout church history, church groups have developed Creeds to specify what a Christian believes in simple terms.
That's all I'll say for now. Watch the video below and realize that creeds really are important.