The Trinity is the doctrine that states that there is one God that is three distinct persons (Father, Son, Holy Spirit)

The Trinity is not one God that is expressed in 3 faces or modes. This would be the heresy known as modalism, sometimes referred to as Sabeillianism or patripassionism, where the Father, Son and Holy Spirit are just 3 different modes of the one God. The often cited analogies of water-vapor-ice and father-son-husband are not accurate representations of the Trinity but are examples of this heresy.

The Trinity is not one God, the Father, with lesser created divine beings such as Jesus. This is the heresy known as Arianism. It is the belief of today’s Jehovah’s Witnesses.

The Trinity is not three separate gods known as the Father, Son and Holy Spirit. This is the heresy known as tritheism or polytheism. It is the belief of many Mormons.

Scriptural Support for the Trinity God is one (monotheism): Deuteronomy 6:4; 1 Kings 8:59-60; Isaiah 45:5,18 Mark 12:29; 1 Corinthians 8:4-6; James 2:19 The one God contains a plurality: Genesis 1:26-27

The Father is a distinct person: Matthew 11:25-27; Matthew 26:39; John 14:16-17
The Father is God: Psalms 89:26; Isaiah 63:16; Matthew 6:9

The Son is a distinct person: Mark 1:9-11; John 17:1-5
The Son is God: Romans 10:9,13 (cross-ref with Joel 2:32); 1 Corinthians 8:6; Titus 2:13; John 20:28; John 8:58 (cross-ref with Exodus 3:14, the great I AM); John 1:1-3, 14
Hebrews 1:8-12 (cross-ref with Psalm 102:25-27)

The Holy Spirit is a distinct person: John 14:26; John 15:26; Matthew 28:19; 1 Peter 1:1-2 1:9-11; Matthew 26:63-65
The Holy Spirit is God: Acts 5:3-4

Jesus is fully human: Philippians 2:5-8; Mark 13:32; Mark 15:33-34

The New World Translation of the Bible, used by Jehovah’s Witness’, removes many Trinitarian references by use of subtle word changes. These changes are not in line with the opinion of the vast majority of scholars throughout the years as is reflected in most other translations of the Bible. One of the most obvious and important changes can be found in John 1:1-3

Revised Standard Version
(1) In the beginning was the Word, and the Word was with God, and the Word was God. (2) He was in the beginning with God; (3) all things were made through him, and without him was not anything made that was made.

New World Translation – Jehovah’s Witness
(1) In [the] beginning the Word was, and the Word was with God, and the Word was a god. (2) This one was in [the] beginning with God. (3) All things came into existence through him, and apart from him not even one thing came into existence.

The world “Lord” in the NT, used to refer to Jesus, is the Greek word “kurios”. This is the same word that the Greek translation of the OT (i.e. the Septuagint) used to translate the Hebrew YHWH (the name of God). The NT writers were declaring that Jesus is YHWH. See Romans 10:9,13 and Joel 2:32