When we say the Apostles' Creed, we join with millions of Christians through the ages in an understanding of God as a Trinity—three persons in one: Father, Son, and Holy Spirit. From early in our Judaic roots we've affirmed that God is one and indivisible, yet God is revealed in three distinct ways. "God in three persons, blessed Trinity" is one way of speaking about the several ways we experience God.
We also try to find adjectives that describe the divine nature: God is transcendent (over and beyond all that is), yet at the same time immanent (present in everything). God is omnipresent (everywhere at once), omnipotent (all-powerful), and omniscient (all-knowing). God is absolute, infinite, righteous, just, loving, merciful…and more. Because we cannot speak literally about God, we use metaphors: God is a Shepherd, a Bridegroom, a Judge. God is Love or Light or Truth.