Hi, sirgodfrey, and welcome to the forum. The whole "God is One" but He said, "Let Us make man in Our image" thing has been a source of confusion since the dawn of time. But the answer is evident in the scriptures, if only we'll look for it, and take Yahweh at His word. He is One---that is, there is only one "God." His self-revealed name is YHWH, which means "I am," though we aren't to translate names, only transmit them. The idea of a "trinity" is slightly off the mark, for it leaves the impression that there are actually three Gods, or as the hymn puts it, "God in three persons." That's not precisely correct, though "God the Father," "God the Son" (Yahshua, popularly known as Jesus), and the "Holy Spirit" (Hebrew: Ruach Qodesh) all exist and operate in our lives. But the reality is simplicity itself, though it may seem complex at first.
As I said, there is only One God, YHWH. "He" (although the gender characterizations we use for convenience aren't really physical characteristics of deity) manifests Himself to mankind in a number of different ways. As you may have noticed, there is a recurring six-plus-one pattern woven throughout scripture, always used to reveal God's plan to us (the creation week plus day of rest, the work week plus Sabbath, etc.). I was therefore not at all surprised to find precisely six "manifestations" of deity through which YHWH revealed Himself and His plan to mankind. They are:
(1) The "Son" of God, Yahshua, who walked the earth as a human being from his birth in 2 BC to his death, resurrection, and ascension in 33 AD.
(2) The "Holy Spirit," who (as promised by Yahshua) indwells the lives of His believers, giving eternal life to our souls, comforting, consoling, and convicting us.
(3) The Shekinah, the "glory of God" who was manifested as light, fire, smoke, and possibly other physical phenomena. Examples of this form would be the burning bush of Moses, the pillar of fire and smoke the Israelites followed in the wilderness, and the "smoke" that filled the Most Holy Place of the Tabernacle.
(4) The "Angel (i.e., messenger) of Yahweh" such as the being that discussed parenthood with Abram and Sarai, and perhaps the One who conversed with Adam and Eve in the Garden of Eden. I'd guess that Melchizedek was such a messenger.
(5) The risen or glorified Yahshua, clearly not the same type of being as his mortal human manifestation. We see Him first on the Mount of Transfiguration, then for forty days after His resurrection, then reigning on earth during the Millennial Kingdom and throughout eternity.
(6) Finally, there are scattered non-human physical manifestations of diety recorded in scripture, such as what Ezekiel saw (1:28) or what John witnessed in Revelation 4.
They're all YHWH---they're all manifestations of the One God, presented different ways to achieve different purposes and communicate different things.
kp