The devil is not a human. He is more powerful than a human. He has the power to do certain things. In this sense, he possessed a snake and used this disguise to convince Eve that she should sin against God. Eve, thinking that the snake was trustworthy, sinned against God (Adam along with her) and released sin into the world.
The talking snake wasn’t an actual snake, rather it was the devil in disguise. Also, most of our beginnings, when attempted to be backed by science, falls short of the logic that we were created by an all powerful being. I don’t want to argue, I just want to point out facts and logic. A metaphorical sense of our beginning is this: do you think that a book can write itself? If so, science would make sense in these terms. If you don’t think a book can write itself, faith in God and the Bible make more sense. I just want to tell you that God loves you, and all you have to do to live in eternal paradise with Him is to believe in Him and repent from your sins.
