Trinity of God is a mystery theologians debated for centuries. And yet just because we can’t fully understand it, doesn’t mean it’s not real. There are a lot of things in nature we don’t understand, but that doesn’t stop us from appreciating them or believing they are real.
One idea that might help with understanding the Trinity though, would be to look at ourselves. The Bible says people were created in the image of God. Just like people consist of three parts, body, soul, and spirit, so does God. You could think of Jesus as the Body of God, Father as Soul, and Holy Spirit as Spirit. Jesus said multiple times that Him and the Father are One, and that those who have seen Him have seen the Father.
A lot of things in the universe come in threes. Space has three dimensions: width, length, and depth. Time has three dimensions: past, present, and future. Every object in the universe consists of three things: mass, energy, and information (like color, texture, etc). The Bible says that anybody can see that God exists, just by looking at nature, even people who have never heard the gospel. That is if God created the universe, we should be able to see His fingerprints in nature. From nature, we could see not only that God exists, but who this God is. When we see how the universe is designed in threes, we can see that God who created it is triune.