Catholics are first and foremost, Christians. We believe that God revealed Himself to us in His Son, Jesus Christ (which is where the name Christians derives from). However God has also revealed Himself to be a Trinity of Persons: the Father, the Son and the Holy Spirit.
The mystery of the Trinity may well be unfathomable and is certainly difficult to explain. God is three persons, but there is only one God.
When God acts upon creation, all three Persons of the Trinity are understood to have acted, but the Church understands that certain effects of the action remind us more of one divine Person than another and so the Church ascribes particular effects to each divine Person.
We therefore speak of the Father as Creator, of the Son, the Word of God, as our Saviour or Redeemer, and of the Holy Spirit, who is the love of God, as our Sanctifier.