There is one God in three distinct divine Persons: Father, Son and Holy Spirit. Each Person is fully God. They are not three gods, three parts of God or three roles that one Person takes turns playing.
A little more context
The Trinity is a mystery God reveals, not a puzzle that a household analogy can fully explain. The Son becomes human in Jesus Christ; the Father does not become the Son. The Holy Spirit is a divine Person, not merely an impersonal force. Catholic prayer begins and ends within this relationship of love.
A practical beginning
When you make the Sign of the Cross, say the words slowly. Let this familiar action remind you that prayer is directed to the living God, even when your understanding is still growing.
Source & further reading
Catechism 232–267: the Holy Trinity (opens in a new tab)↗Teaching summaries are introductions. Follow the linked Church source for its fuller context.