It is good when you want to learn, but from reliable resources. The basis for the study about God could be got from the bible. It is the first and the most genuine source as it never contradicted all thruogh the generations.
The book of Gen1 verse 1 reads : "In the begining 'God', " The word 'God' that appeared was from 'Elohim' which is a plural word for God.
Psalms 139 also tells that God is omnipotent, self existing and non-reliant, but why would he have said "let 'us' create man in 'our' own image". The answer is in 1John5:7 that God the Father, God the Son, and God the Holy spirit are one.
But the question of how three personalities can be one could be explained by:
1. They are distinct from each other and not separate e.g Jesus telling His disciples when they asked Him of the Father, He said since you know me, you know the Father
2. The closest (most probably,) example you can give for 3 in 1 personality is your distinct Spirit, Soul and Body.
Mind you, Christianity is not a rational field, Paul said: the gentiles seek after wisdom and the jews after signs but God as used the little things of this world to put to shame the big ones. THE FOOLISHNESS OF GOD (which man address to be so) IS BETTER THAN THE WISDOM OF MAN.

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