Grammar correction: "What's the difference between..."
1. People is the plural of person, it is casually used to refer to all or specific groups of human beings. The usage is the most universal in modern English.
2. Human is more scientific, and can be both a noun that means the same as 'person', or an adjective, as in 'human nature' or 'human societies'. It would sound odd to refer to the people in your life as 'humans', and is more often used in fiction when we are spoken of by other species, most often aliens. Eg. "Humans are so strange, they destroy the planet they live on with nowhere else to go!"
3. 'Human beings' is only used as a noun. It has a more poetic sound than 'people', and is usually used to compare our species to others. For instance: "While dogs have to rely on non-verbal signals, human beings have developed a wide-range of linguistic abilities to make themselves understood".
4. Person is the singular form of 'people'. It can be used to indicate someone when you don't know their name or gender. "The person who left this pen here had better come fetch it before I lock up!"
Please message me if you have any further questions ^_^