What are the Creeds?

The Holy Trinity is called a mystery because
no one understands fully what they mean.
The Catholic Faith tries to help us understand

What are the creeds?  What do we mean when we Catholics make the sign of the cross?  Many Catholics don't even know why they do it, and even I benefited from some recent research into this.

We usually do the cross, and say the words: father, son, and holy spirit.  But what is the father, what is the son, and what is the holy spirit?  What is the relevance of them? Why do we say them?

Well, it all starts with God, and God is a Trinity of persons as follows:

1. Father
2. Son
3. Holy Spirit

What they are is part of a creed, which comes from the Latin term "credo," which means "I believe." Theology, Catholicism, essentially focuses on the study of God as the Holy Trinity.  We cannot fully understand this.  However, God has revealed it as the basis of our Faith.  All other things spring from this essential mystery.

Let me further describe the Holy Trinity:

1. God, the father, or Lord.  He is the origin of everything and cares for us as children.  He sees all and knows all.  Everything in the universe comes from Him. God is almighty because he can do all things.  He is granted infinite mercy to us, and even allows us to make our own decisions, even to disobey him, and cause sin.  The ultimate goal of God is for people to believe in him in order to conquer evil and bring life from death, which he ultimately did when he allowed the Word to become a human, to live among us, to share the word of God, and to die for us so that we may live. 
2. Son of God, the Word, Jesus.  He is the wisdom of God.  I like to simply refer to him as "The Word," as you can read in John 1:1.  The word appeared at random times in the Old testament, as it was He who created the Sun and planets, the Earth, Light/Day, Darkness/ Night, and man in the image of the Father.  He later appeared to Moses in a burning bush.  Yet he most famously appeared as Jesus Christ.  His mission, the words mission, is to share the wisdom of the father.  
3. Holy Spirit or Advocate of God:  This is what sanctifies us.  This is what we feel inside us.  Without the Holy Spirit, we cannot accept God.  The Holy Spirit is the sense of Glory, Faith and Hope inside us.  It's the feeling of love, joy, and happiness.  

Now Consider what the John the Apostle had to say about the Word:

In the beginning was the Word, and the Word was with God, and the Word was God.  He was with God in the beginning. Through him all things were made; without him nothing was made that has been made. In him was life,and that life was the light of all mankind. The light shines in the darkness,and the darkness has not overcome it. (John 1:5)

The Father , Son/word, and Holy Spirit are the central mystery of our faith, yet together they make up one God.  All that is done, all that is created, comes from the Father, through the Son, and in the Holy Spirit.  Those who believe are Christians.