"The doctrine of the Trinity means that there is one God who eternally exists as three distinct Persons — the Father, Son, and Holy Spirit.
This is a good definition that represents the orthodox (lowercase o) and Western understanding of the Trinity. Basically, there is one divine being called God, and three distinct persons who are that one and undivided God. A similar definition that represents the Eastern understanding of the Trinity would be this: There is one God, the Father, who beget a Son and breathed out a Spirit, and the Son and the Spirit share the same undivided, divine essence as the Father. Like in the Western understanding of the Trinity, the Father, Son, and Holy Spirit are three distinct persons in the Eastern understanding.
From a Trinitarian perspective, the person of Jesus of Nazareth is the same person in the Trinity who is known as the Son. Considering that the Son is God in the sense that his essence is the same as God the Father, it is correct to say Jesus was God (yet also human).
If by
God you mean the Father, then no. Considering that the Father and the Son are two distinct persons, the Father was not Jesus.
Was Jesus the spirit which existed before he did or was he a new spirit?
I'm not sure what is meant here by
spirit.
No. God the Father cannot be his own Son, 'personhoodwise.'
Is the spirit god and jesus or are god and jesus the spirit?
Again, I'm not sure what it meant here by
spirit.
If God is a single being, he can’t be 3 separate distinct persons. That is grammatically incorrect.
No, it would be nonsensical to say God is a single being and three distinct beings, or a single person and three distinct persons.