each is a determiner and pronoun used to refer to every one of two or more people or things, regarded and identified separately.
Common usages of each:
1. As a determiner: "Each student has their own locker."
2. As a pronoun: "The apples cost 50 cents each."
3. In combination with "other": "They looked at each other."
4. In expressions like "each and every" for emphasis