In Genesis 1:26 we read "Then God said, 'let us make man in our image, after our likeness.'" Christian theology says that "us" refers to the Trinity -- the Father, Son, and Holy Spirit. The author of Colossians says (in 1:16) " For by him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities—all things were created through him and for him," implying that Jesus was there at the beginning. John 1:1-3 implies the same thing (while embracing the doctrine of the Logos, a topic for another time). While there are theologians who dispute the doctrine of the Trinity and claim that the New Testament doesn't support it, the fact that the New Testament claims that there is a Father, a Son, and a Holy Spirit seems indisputable. The idea that they are three yet somehow one is, admittedly, confusing, and the Nicene Creed says (for all practical purposes) it's implied, so just accept it without trying to understand! But it's easy for a Christian to see the "three" here and impose that upon Genesis.

As I've discussed before, the writers of the first books of the Bible were henotheistic. They believed that there were multiple gods, but that they were to worship only their god, Yahweh aka the LORD. Deuteronomy 32:8-9 makes it clear that the Most High god gave the nation of Israel to the LORD as an inheritance. The other gods got other nations as their own inheritance.

Christians impose the beliefs of New Testament times (and beliefs of today that may not even be consistent with the New Testament) upon the Old Testament / Hebrew Bible under the false belief that it must be 100% consistent. It isn't. The Hebrew Bible is it's own book and has been co-opted by Christians. This is unsurprising, since the New Testament church comprised, at first, Jews, and came out of Judaism. But the idea of "God" had evolved throughout the ages that the Old Testament spans, and the idea that there is only one god coalesced somewhere in the middle, by the time of the story of Elijah and the prophets of Baal. At that point, Baal had become a false god, rather than simply the god of another nation.

In Genesis 1, "us" means "the Most High God and the sons of God."

When you read the Bible, you need to read it to see what it actually says, rather than trying to force your beliefs on the whole thing. Christians claim that their beliefs come from the Bible, but the opposite is actually true: Christians start with their beliefs, then try to make the Bible fit. And it's not even the New Testament that they're starting with -- it's 21st Century beliefs. If you want to try to be Biblical in your beliefs, you're going to have to start at the beginning and read the book, noticing when the notions you have -- the things you've been taught your entire life and those you've come to believe over the years -- don't align with the text you're reading. If you won't do that, can you actually say that you're studying to show yourself approved, or that you're searching the scriptures to see what is true?