This is what I believe about God, Jesus and the Holy Spirit.
God, Yahweh, is the supreme creator. Aeons ago he created his only begotten Son. Now whether that's Son's name was Michael the Archangel, I don't know, but we know that the Jews looked forward to the Messiah coming, at least some did. I believe Jesus was born from a virgin, Mary, he gave his life for us, then was reanimated to his old position. He then became known as Jesus Christ. The Holy Spirit is God's energy, and with it He can make his presence felt anywhere in the universe.
As for the defintion of "spirit" there are so many interpretations. For instance, I can tell someone, I can't be there in person, but I am "with you in spirit" - it's a saying, that I can't be there with you, but know that I wish to be. Then there's spirits, life forms which inhabit the heavens. The Bible talks about a lying spirit and the spirit that "now operates in the sons of disobedience." So it's difficult to know exactly what Paul meant at times when he makes reference to "spirit"
AGuest,
I don't really think of the Holy Spirit as a "third person or entity" - it's God's force.
I have potential energy to do things, but I don't think of the calories I burn doing something as a person or an entity.
So for that matter, it's really two individuals, God, the Father, and his Son.