ALL THREE were involved in creation

John 1:1-3 NIV In the beginning was the Word, and the Word was with God, and the Word was God. He was with God in the beginning. Through him all things were made; without him nothing was made that has been made.

Genesis 1:1-2 NIV In the beginning God created the heavens and the earth. Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.

ALL THREE were there at the conception of Jesus

Luke 1:35 NIV The angel answered, “The Holy Spirit will come on you, and the power of the Most High will overshadow you. So the holy one to be born will be called the Son of God.

ALL THREE were there at the launch of Jesus's ministry

Luke 3:21-22 NIV When all the people were being baptized, Jesus was baptized too. And as he was praying, heaven was opened and the Holy Spirit descended on him in bodily form like a dove. And a voice came from heaven: “You are my Son, whom I love; with you I am well pleased.”

Jesus put ALL THREE on the same level

Matthew 28:19 NIV Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,

There are more verses to support the Trinity.