King James Version of the Bible

Today we started the King James Version of the Bible. We had to read several of the first chapters of Genesis, which tells the stories that most of us already know, no matter how deeply. I have several comments. For example, on Chapter 2 the creation of the woman is being told. On Section 24 the following passage is written: "Therefore shall a man leave his father and mother, and shall cleave unto his wife..." I found this interesting because I do not understand how the concepts of father and mother already existed, based on the idea that Adam and Eve were the first human couple on Earth, making them the first parents. Also, in Chapter 3 Versicle 1 the snake says to the woman that the forbidden fruit will give her the ability to recognize good from evil, finally tempting her into tasting it. In a way, what the snake said was true. When they ate the fruit, Adam and Eve were banned from the Garden of Eden, and this somehow made them realize the difference between good and evil. Well, not exactly evil, but the difference between good and bad, because they realized that the place in which they had been living in was a paradise and they now had to face difficulties. Finally, in Chapter 4 Versicle 17 we are told about Cain´s wife, which made me wonder where she came from. Adam and Eve were supposed to be the only humans, and the Bible never mentions that they had any daughter that could become his wife. I hope that someone might be able to give me an anser, because I honestly find it very confusing.