Some things in life are just mysteries. For example, how does an airplane that weighs tons fly into the air taking along with it numerous passengers who weigh a lot combined? Or how does a ship weighing tons go off into an ocean and float even though each of its individual parts would sink like a rock? Or how does electricity get from the wires attached to the poles outside my house and get to the switches that I can just through at my beck and command to light up the rooms and cool down the house?
You may say that those things can be explained with aerodynamics and buoyancy and electricity explanations to which I cannot give name but to me they are still mysteries. Even if you were to try to explain to me why these things work, I would still wrinkle my forehead and grunt, "Huh?" in a Scooby-Doo kind of voice. Your explanations do not make sense to me because I do not have a working knowledge of the dynamics and concepts with which you may make your explanations.
The idea of the Trinity is also a mystery, to me and everyone else alive, regardless of how one may try to explain it. The concept of the Godhead being Three in One, Three separate beings residing in one form, but serving with three functions unique to each is mind boggling. I have heard preachers try to explain it by giving comparisons to eggs having three parts but still being one (shell, white, yolk) or water being in three forms (water, ice, steam) even though it is ultimately just water. All of these pale in comparison to an explanation of how God can be three separate beings but also be one being combining all three into one.
Those in the Early Church formulated the Doctrine of the Trinity and tried to explain it and when they put together the Nicene Creed in 325 or so, they tried to say what they thought about all three members of the Godhead, giving lots of type to Jesus and several lines to God and a few to the Holy Spirit. Most likely, they only knew what they knew about God or the Holy Spirit because of the life of Jesus Christ. That is what Jesus told his disciples about the roles of the Trinity also. He said if you had seen Jesus, you had seen the Father. Then he said that if you listen to the Spirit, it will tell you about Jesus. So, Jesus is in the center and is the glue holding the Trinity together. We cannot really know much about either of the other two unless we know who Jesus is and what he taught that was important.
When I was growing up in the fundamentalist church that I grew up in, the concept of God presented to me was one of a terrifying being that wanted to do me harm and it was only because Jesus stood between me and God and prevented God from seeing me that spared me from eternal damnation. God was always ready to throw a lightning bolt at me and wipe me out, but Jesus stood there ready to present God from harming me. No wonder we liked to sing, "What a Friend We Have in Jesus." He was like our big brother trying to protect us from that big bully named God the Father.
Once I left that church and had a few years of counseling under my belt, I sorted out the truth about the Trinity and found out that the God of the Old Testament (that fearsome, awesome being out to get us) was actually a God of steadfast love showing mercy to the 1000th generation. God was like someone who would hold an infant to his cheek. God was like an eagle that would spread its wings around us to protect us. God was like a good parent wanting to do good things for his children. God was not a big bully but was actually just like Jesus, trying to take care of us and show us he loved us.
So, the doctrine of the Trinity may be hard to explain but the ones represented in it are not. God is merciful and kind. God is loving and forgiving. Jesus is just like God. The Holy Spirit reminds us of all this. Maybe it is not that hard to explain or believe when you break it down into understandable parts.
Now, trying to understand how that big jet can fly.....that may take a while.