The Father is God, the Son is God and the Holy Spirit is God, that's who they are, Deity. It is their nature that makes them co-equal, co-eternal because there is only "ONE" God by nature. You ask "three whats exactly," it's not three whats but three person's within the Godhead that make up the one God. And "Godhead" simply means "Deity."
Now, I've said this more than once to you churchmouse. What you have in common with your parents and all the rest of mankind is we all have the same exact "nature," i.e human being. In other words, your nature distinguishes you from all that are not human beings, animals, birds, mamals, fish insects and God. And because of God's nature of "Deity" this is how He is distinguished from all that is not God. Furthermore, (and like I have explained more than once) God chose to "identify" Himself in the Scriptures as three persons who are one in unity as well.
IN GOD THE SON,