For example, horror films are a genre. Horror novels belong to the same genre as horror films because they share similar organization and language, the same audience and have the same purpose…to scare you.
An essay on a horror film, however, is a different genre because it has a different audience (academic) and a different purpose (to educate/inform) than the film or novel.
So genre analysis is the ability to identify a genre’s defining organization, language, intended audience and purpose.