The Holy Spirit is God, one of the Persons of the Trinity. Jesus states His oneness with the Spirit in John 14.16-18. He is put on an equal par with the Father and Son in Matthew 28.19; 2 Cor. 13.14 et al. Hopefully that helps.
In the NT His role is described as:
- He lived in Jesus and empowered Him for ministry.
- After the resurrection, the Spirit is freed to be the Spirit of Christianity as a permanent arrangement.
- He is the functional equivalent of Jesus on Earth
- He indwells believers
- He is a Counselor and guide for Christians
- He advocates our causes before the Father
- He prosecutes the world, showing people their sin and convicting them of it.
- He makes sure there is always a testimony about Jesus on Earth.
- He guides people into truth about God and Jesus.
- He inspired the writings of the NT.
We can talk about this more if you want.