I was taught God is Trinity as a child. When I grew up to about 24 years old I encountered a church that taught God is One or Oneness. Then I met a church that taught God is Two , the Father and the Son. Then another church taught that Jesus is not God. I was confused to say the least. So I made my own research, if God is One only then who is our Lord talking to ? If Jesus is not God, why is there Scripture that says God said to the Son, thy throne O God...To make a long story short, I took the stronger of verses like when Jesus said my Father is greater than me and while other verses like when God said to the Son, thy throne O God..Then I took the latter verse which is stronger besides Jesus could be talking as a man in the former verse.
On the Holy Spirit, I remember a verse that says Blasphemy against the Holy Spirit will not be forgiven here ,now and forever.
On understanding the concept of Trinity , I learned not to overanalyze.And I tried not to add and subtract from it. I prayed to God I will just simply believe the way it was written. And from reading the Bible, there is Father, there is Son, there is Holy Spirit, and I believe it. And I am no longer confused. When I glorify one of the three I glorify the other. So glory be to the Father, the Son and the Holy Spirit, one God forever and ever , Amen.
By the way, some asked how can one plus one plus one be one?. Some answered too, but one times one times one equals one.
Can we the creatures put our Creator in a box or fully explain who He is ? our answer most likely be no but we can know Him by His revelation of Himself through the written Word, the Bible , and the Word that became flesh and lived among us and through the Holy Spirit who helps us.