Each means every single one considered individually. When your teacher says “each student needs to bring a pencil,” she's talking about every student, but focusing on them one at a time rather than as a group.

The difference between “each” and “all” matters. If someone gives cookies to all the students, they might hand out one big box to share. If they give a cookie to each student, every individual person gets their own. When a coach says “each player will get a turn,” he's promising that no one will be left out: your turn, my turn, everyone's turn, counted out one by one.

You'll often see “each” paired with singular words. We say “each person has” (not “have”) and “each book costs” (not “cost”) because we're thinking about them individually, even when there are many. When your parents say “each of you is responsible for your own homework,” they're making clear that this isn't a group project: the responsibility belongs to each of you as an individual.

The word helps us be precise. “Everyone should do their best” talks about the group as a whole, while “each person should do their best” emphasizes individual effort and accountability.