If you're saying "everyone" broadly, you would say "alle." 'Alle haben einen Apfel' would sound like 'Everyone has an apple,' as in this vague group of people has a single apple just sitting in their midst.
If you're saying everyone with respect to each person as an individual, literally "every one," it's jeder. 'Jeder hat einen Apfel' looks like every single person addressed has one apple each.
For the most part alle/jeder is a tonal difference when talking about people.
Alles, however, literally means "everything." You normally wouldn't explicitly refer to people as things. It's more for making general statements. "Do you have everything." "Everything is fine" etc.