This is what I understood from the teachings of the Catholic Church:
There are sacred mysteries which are not explainable by rational or scientific reasoning and thus believing in these mysteries is the catholic faith.
So the Trinity means God, Jesus and the Holy Spirit are separate and the same.
Resurrection is special because God lived as a human, died to cleanse the sins of all humans (dying is a punishment for the sins) and his resurrection means he is really God, he cannot die and doing so he defeated death itself. Which means all humans believing in God will be able to cheat death and live eternally in paradise.
God died for our sins because he loves humans and wants them to be free of sin.
Trying to understand this through reason is not possible. You need faith, this is the whole shtick.
Again this is my understanding, been a long time since I went to catechism.
My mistake its catechesis not catechism. English is not my first language.