AP stands for the Associated Press, which is a news agency. AP style guidelines are widely used by journalists. The latest edition of the AP stylebook is the 2019 edition.
Unlike for MLA, APA, and Chicago citations, AP guidelines don't ask you to include in-text citations or footnotes. Instead, you should include information about your sources in the actual wording of the sentence.
Purdue OWL on AP style guidelines
Presentation from CSU Bakersfield with AP examples