Can you explain the Trinity, please?

I do have faith in the Trinity, though I don't understand it. Crucifixion is a horribly painful way to die. God could so easily simply forgive all sins without crucifixion. Jesus, being God submitted to this death. But, it wasn't necessary. I still have trouble understanding how one God could have three Persons. Why not say, that God can take any form He wants? Did God the Father have to be in Heaven at the moment of God the Son's death? How can God die? Who would raise Him from the dead?