info about that on Wikipedia. I also won't be explaining why I believe the Bible is true. That's a different question for another time. My main aim here is to give a basic idea of what the doctrine of the Trinity is and show some of what the Bible actually says that relates to it.
The word 'Trinity' doesn't appear in the Bible but it's a doctrine that pulls together two big things that the Bible repeatedly and clearly says about God. You can hit the links and see for yourself...
1. The Bible says that God is one (Deuteronomy 6:4, Mark 12:29) and that there is only one God (Deuteronomy 4:35, 32:39, Psalm 86:10, Isaiah 43:10, 45:5, 1 Timothy 1:17, 2:5).
2. The Bible also clearly teaches that the Father is God (John 6:27, 1 Corinthians 8:6), that Jesus is God (John 1:1 and v14, John 8:58, 10:33, 20:28, Romans 9:5, Titus 2:13, 1 John 5:20) and that the Holy Spirit is God (2 Corinthians 3:17-18, Acts 5:3-4).
So the Trinity doctrine summarises these clear teachings of the Bible by saying that God is three in one (tri-unity - from which we get the word 'trinity'). God is Father, Son and Spirit and each of these is fully God and yet they are not three gods but one God.
Personally, I'm overwhelmingly glad that God is the perfect family. He didn't create because he was lonely but because he already enjoyed perfect loving relationship within himself (1 John 4:8) and wanted us to be part of it (John 17:20-23).