How can Jesus be God, the Spirit be God and the Father be God?
But instead of going into all the details, there is more to you, than just you.
There are other beings or person, that are a part of you, that affect what you say and how you feel, and so on.
We are made like God, and like God, we have more than just us abiding in us.
Some of the other voices or thoughts we hear and can quote, are not from our conscious brain.
And some of the actions you take, are not from the conscious you who is doing it.
These other beings, though they are lesser than you, are still apart of who you are today.
If you could separate your spirit from your soul, you would have two different, yet the same people.
Your spirit man makes up apart of who you are, as does your heart.
Each of them are you, and yet, each are there own person.
But without one of them, you would be a different kind of person, with different likes and dislikes, thoughts, and so on.
And God is no different, only He can subdivide each part of Himself, if I can put it that way.
So God is indeed three beings, making up One God, and thereby making Him the way He is.