We might say, "the police" to refer to all of them everywhere, or to all of them in one office, or even to a group of them "over there" or whatever. We might also say "the cops". "Cop" is maybe a little less formal. Also, I think it has a very slight negative connotation, as of someone who does not like the police. Moreover, in English you cannot say, "a police". You can say, "a police officer". Also, you can say, "a cop", as in, "Are you a cop?" If someone works at a police station as a police officer, we would say, "He is a police officer," or maybe, "he is a cop". But again, saying "cop" does not sound as respectful, at least to me. "He works for the police." "He works for the cops." The second sentence has the same negative connotation, but it is correct. However, saying "works for the police" doesn't necessarily mean one IS a police officer. For that, one would say, "he is a police officer." "Someone in my family is a police officer/is a cop." "By brother is a cop." "My sister is a police officer." "My uncle works for the police." (He might be an informant.)

He works for the police/police force as a policeman/police officer. Cop/copper can be seen as negative as already mentioned.

Policing is a general term.The Americans like to call their police cops.Being a police in a different country is the same as being a cop in America.

Today, ‘cop’ is not considered derogatory. It is less formal and shorter (and therefore more common) than ‘police officer’. Addressing anyone by their job is generally considered a little rude, and that’s also true of ‘cop’. More polite is ‘officer’. ‘Officer, can you help me?’ ‘Her husband’s a cop.’ ‘She works for the police department.’ ‘She’s a police officer.’ ‘Careful. The cops are ticketing on I-90.’