Hello Julia! Thank you for your question. I think for the word people, it is more common to use the word "οι άνθρωποι" in nominative and "τους ανθρώπους" in accusative. "Το άτομο" means a person, an individual. "Ο άνθρωπος" means a human being. In an informal context, if you want to call a group of people you can use the word "παιδιά". It is like the word "chicos" in spanish, "gente" in brazilian portuguese or maybe like the word "leute" in german.

to say people is better to use the term ανθρωποι ατομα means individuals

Τα άτομα means the persons (like 3 persons/people, 4 persons etc). Οι άνθρωποι means the humans/the people. Ο κόσμος means people, as well. As in “there are many people at the beach”. I hope I could answer your question. * ανθρώπους is the accusative form of οι άνθρωποι.