We use 'police' to mean the whole organization that enforces rules. It refers to the group, not just one person. It works as one unit.
The police are investigating the crime.
The police have new rules to follow.
To police means to watch people and make sure they follow rules. It often means control in public places or at events to stop problems.
They police the crowd at the concert.
The guards police the border well.
Some places have special police groups. They watch and protect the area, like malls or stadiums, from problems and fights.
The mall has its own police team.
The police at the stadium are very alert.
To police can mean to watch and correct language or behaviour carefully. For example, a teacher might police grammar to keep it correct.
The editor polices grammar errors well.
Teachers police students' spelling mistakes.
To police means to watch and stop illegal or dangerous items from coming in or out. This happens at borders or airports to keep people safe.
They police the border for illegal guns.
Customs police the airport for drugs.
Sometimes people say 'police' meaning one police officer. It is informal or used in news headlines. It means a person who works to keep law and order.
The police caught the bad man.
The police helped the lost child.
