The noun человек has an irregular plural – люди. This is just like in English how person becomes people in plural. But an alternative plural does exist – persons, which we use mainly in very formal contexts.
Anyway, when declining, take dative plural for example, either людям or человекам is possible.
How do we know when to use one over the other?
| When referring to people in general, use люди and its declensions. When using numerals or some, many, etc., use человек with its proper plural declensions. |
Confused? Look at this table for better understanding:
| человек [person] |
| plural forms only |
| nom. | gen. | dat. | acc. | inst. | prep. |
|---|---|---|---|---|---|
| люди | людей | людям | людей | людьми | людях |
| люди | человек | человекам | человек | человеками | человеках |
Now, let’s observe some examples:
| Мне нравится помогать людям с русским. I like to help people with Russian. |
| Я разговариваю только с добрыми людьми. I speak only with kind people. |
| Он пишет о знаменитых людях. He writes about famous people. |
And compare those ones with these:
| В вашей семье сколько человек? How many people are in your family? |
| В США живёт больше 300 [трёхсот] миллионов человек. Over 300 million people live in the USA. |
| В статье речь идёт о 7 [семи] разных человеках. The article is about 7 different people. |
Well, I hope this helped you better understand which plural form to use in any given situation.
My Slavic Studies 