For a Catholic, apologetics is a three-layered art. You have Natural Apologetics, followed by Christian Apologetics, and finally Catholic Apologetics.
Natural Apologetics is concerned with what can be known by reason alone, apart from revelation. Natural Apologetics addresses the question: Does God exist? This method of apologetics is what a Christian might use to engage in dialogue with an atheist or agnostic.
Christian Apologetics starts with God’s existence, then asks: Who is God? With the many world religions, Christian Apologetics has the task of showing that God is the Trinity: The Father, the Son, and the Holy Spirit. A Christian would use this when talking with non-Christian theists.
Catholic Apologetics takes the existence of God, the knowledge of who God is, and asks: What Church did he establish? A Catholic would use this form of apologetics with non-Catholic Christians to show that the Catholic Church was founded by Jesus.