A formal term for a member of the police force, used in official contexts and news reports. In casual conversation, お巡りさん or 警官 are more common.
A police officer is directing traffic.
He is studying to become a police officer.
He says he wants to become a police officer in the future.
He was caught by a police officer for speeding.
I was stopped and questioned by a police officer while walking late at night.
警察官 specifically and formally denotes an individual police officer, whereas ポリス is a casual, katakana-flavored term that can mean either the force or an officer.
警察官 means a police officer in general, while 捜査官 specifically denotes someone conducting criminal investigations.