Why are people mad that Joe Biden won the election?

Hey I’m 5 and My Daddy says I’m very smart for my age and he also says you all are very smart! That’s why I came to ask u this question. I keep hearing people say that Biden won the election but my daddy says it’s not true and I’m wondering who is right. He also says people are mad about it but I don’t understand why it would matter who wins. My teacher has brown hair so I guess that’s kind of what I picture the president looking like but my daddy says that’s not really what he looks like so idk.