What does it mean when the Catholic Church makes someone a Saint? I come
from a protestant background and we don't have any Saints to my knowledge.
I've been to a non Christian Church called St Peter's it wasn't catholic but
anyhow who is Saint Peter?

When the Catholic Church calls someone a Saint all this means is that we have recognized that the individual lived an exemplary life of holiness. The person whom is declared a saint often has founded an order within the Catholic Church dedicated to the mission of the Gospel and one often serving the poor. In the history of the Church there is usually two miracles which have to occurred as a result of intercession on behalf of that particular Saint. So for example; if a nun were to pray asking Pope John Paul II to intercede on her behalf to the Lord for a healing from cancer then if that cancer miraculously disappeared without any scientific cause or explanation we can be certain that this miracle can be attributed to Pope John Paul II. This is usually when the Church begins looking seriously at the cause for the canonization of the individual in question. The process of canonization refers to the process where the Church discerns, under the guidance of the Holy Spirit, whether there is sufficient evidence within the life of and miracles attributed to the individual in question.  These event give glory to God and  witness to the power of Jesus Christ. Nothing within the life of the individual contradicts the Catholic faith.

When speaking about Saint Peter we are usually referring to the first pope of the Catholic Church Saint Peter the Apostle. Saints are a great gift to us! They help intercede on our part from heaven where we cannot yet be.
Really a Saint is someone whom we can look to as an exemplary model of the Christian life. We can see in their actions, their writings, and their works the image of Jesus and a life of Holiness. The Church when they declare someone to be a Saint believes that the individual is now in the Kingdom of Heaven with the Lord.  Until the end of time they will pray and intercede on our behalf to make sure we end up in heaven also.  Saints are witnesses to the faith and in a sense role models to us of what it means to be a true Christian.