countability - Is "people" a countable or a non-countable noun?

I saw these sentences on the Internet:

1. 
   

   There are three people here.

   
   


2. 
   

   A few people didn't enjoy the play.

   
   

Now I'm not sure whether people and other collective nouns like team, family and police are countable nouns or uncountable nouns. Is there an explanation for how these words work?