The 3 in 1 Trinity is something as a Christian I struggled with (and still struggle with at times) for years. I never understood who they were or how they "fit" into the equation. Several years ago, it was almost like a light bulb came on for me concerning the "Trinity."
This is my understanding of it from the Christian Biblical teachings I have been taught. (I was initial taught in a Nazarene church but finally understood in a Baptist church, as a point of reference.)
The "Trinity" is the Christian God that is referred to in three separate ways depending on the context of the "need" of the person. He is the "Father" for comfort, support and love. He is the "Son" for the granting of forgiveness and grace. He is the "Holy Spirit" for the understanding, guidance and direction. God is "perfect" and therefore fills all needs through the "Trinity."
At least that is how I finally broke it down in my mind to understand it...