ELI5: Why is everyone saying Biden won when they still haven't counted all the votes?

I don't think he hasn't won, but I don't get why they're saying he won before they count all the votes.<br><br>EDIT: I want to emphasize that I am completely happy that Biden won and I think he will be a great president. I was simply confused about why they were saying Biden won the election before they counted all the votes.