Let me try to explain the concept. It's hard to understand, even for one brought up in the Roman Catholic church. I am not claiming this is absolute truth, but a perception to explain the nature of God. Muslims get bent out of shape, so to speak, at this analogy, but here we go:
1. There is ONE God. One!
2. Jesus was his "son". Now, "son" is a concept I, too, struggle with. Aren't you, too, Allah's son/daughter? His Creation? I prefer to say Jesus was created by God's will.
3. The Holy Spirit. This is the essence created by Our one God that we can perceive. It is the force that moves gravity on earth at a rate of 9.81 m/s/s. It makes electrons revolve around nucleus of an atom, and allows the nuclear fission in our sun that lights our realm, moves that energy to introduce glucose into the environment, and allows our bodies the miraculous ability to heal.
I've ALWAYS been taught there was ONE God. The trinity thing was there to help our feeble human minds grasp a small glimpse of His complexity. ONE God.
The Symbol (Creed) of the 11th Synod of Toledo has been called: ‘The most complete formulation of the doctrine of the Trinity in a Creed since the times of the Fathers.’ This is it:
‘We confess and believe that the holy and ineffable Trinity, Father, Son and Holy Spirit, is one God by nature, of one substance, of one nature as also of one majesty and power.
‘And we profess that the Father is not begotten, not created, but unbegotten. For He Himself, from whom the Son has received His birth and the Holy Spirit His procession, has His origin from no one. He is therefore the source and origin of the whole Godhead. He Himself is the Father of His own essence, who in an ineffable way has begotten the Son from His ineffable substance. Yet He did not beget something different (aliud) from what He Himself is: God has begotten God, light has begotten light. From Him, therefore, is "all fatherhood in heaven and on earth"
‘We also confess that the Son was born, but not made, from the substance of the Father, without beginning, before all ages, for at no time did the Father exist without the Son, nor the Son without the Father. Yet the Father is not from the Son, as the Son is from the Father, because the Father was not generated by the Son but the Son by the Father. The Son, therefore, is God from the Father, and the Father is God, but not from the son. He is indeed the Father of the Son, not God from the Son; but the latter is the Son of the Father and God from the Father. Yet in all things the Son is equal to God the Father, for He has never begun nor ceased to be born. We also believe that He is of one substance with the Father; wherefore He is called homoousios with the Father, that is of the same being as the Father, for homos in Greek means 'one' and ousia means 'being', and joined together they mean 'one in being'. We must believe that the Son is begotten or born not from nothing or from any other substance, but from the womb of the Father, that is from His substance. Therefore, the Father is eternal, and the Son is also eternal. If He was always Father, He always had a Son, whose Father He was, and therefore we confess that the Son was born from the Father without beginning. We do not call the same Son of God a part of a divided nature, because He was generated from the Father, but we assert that the perfect Father has begotten the perfect Son, without diminution or division, for it pertains to the Godhead alone not to have an unequal Son. This Son of God is also Son by nature, not by adoption; of Him we must also believe that God the Father begot Him neither by an act of will nor out of necessity, for in God there is no necessity nor does will precede wisdom.
‘We also believe that the Holy Spirit, the third person in the Trinity, is God, one and equal with God the Father and the Son, of one substance and of one nature, not, however, begotten nor created but proceeding from both, and that He is the Spirit of both. We believe that He is neither unbegotten nor begotten, for if we called Him unbegotten we would assert two Fathers, or if begotten, we would appear to preach two Sons. Yet He is called the Spirit not of the Father alone, nor of the Son alone, but of both Father and Son. For He does not proceed from the Father to the Son, nor from the Son to sanctify creatures, but He is shown to have proceeded from both at once, because He is known as the love or the sanctity of both. Hence we believe that the Holy Spirit is sent by both, as the Son is sent by the Father. But He is not less than the Father and the Son, in the way in which the Son, on account of the body which He has assumed, testifies that He is less than the Father and the Holy Spirit.’
‘This is the way of speaking about the Holy Trinity as it has been handed down: one must not call it or believe it to be threefold, but Trinity. Nor can it properly be said that in the one God there is the Trinity, but the one God is the Trinity. In the relative names of the persons the Father is related to the Son, the Son to the Father, and the Holy Spirit to both. While they are called three persons in view of their relations, we believe in one nature or substance. Although we profess three persons, we do not profess three substances, but one substance and three persons. For the Father is Father not with respect to Himself but to the Son, and the Son is Son not to Himself but in relation to the Father; and likewise the Holy Spirit is not referred to Himself but is related to the Father and the Son, inasmuch as He is called the Spirit of the Father and the Son. So when we say 'God', this does not express a relationship to another, as of the Father to the Son or of the Son to the Father or of the Holy Spirit to the Father and the Son, but 'God' refers to Himself only. For, if we are asked about the single persons, we must confess that each is God. Therefore, we say that the Father is God, the Son is God, the Holy Spirit is God ' each one distinctly; yet there are not three gods, but one God. Similarly, we say that the Father is almighty, the Son is almighty, the Holy Spirit is almighty, each one distinctly; yet there are not three almighty ones, but one Almighty, as we profess one light and one principle. Hence we confess and believe that each person distinctly is fully God, and the three persons together are one God. Theirs is an undivided and equal Godhead, majesty and power, which is neither diminished in the single persons nor increased in the three. For it is not less when each person is called God separately, nor is it greater when all three persons are called one God.’