The God of the Bible is one. The great foundation scripture for understanding this is Deuteronomy 6:4-5 " 4 'Listen, Israel: Yahweh our God is the one, the only Yahweh. 5 You must love Yahweh your God with all your heart, with all your soul, with all your strength."
In order to understand who God is and to know Him, it is tremendously important to know that He identifies himself by a name. That name is written with four Hebrew letters that approximate our "YHWH" in English. The one God of the scriptures identifies himself by that name. In Isaiah 42:8 God tells us, "I am Yahweh, that is my name!" In Isaiah 45:5 Yahweh says, " I am Yahweh, and there is no other, there is no other God except me."
How To Invoke (Call on) God
Yahweh spoke to Moses in Exodus 3:15 and told him that Yahweh was His name for all time and He was to be invoked by that name for all generations to come. "15 God further said to Moses, 'You are to tell the Israelites, "Yahweh, the God of your ancestors, the God of Abraham, the God of Isaac and the God of Jacob, has sent me to you." This is my name for all time, and thus I am to be invoked for all generations to come."