The present perfect tense is used to describe events that occurred at an unspecified time in the past or that began in the past and may still be ongoing. It is formed using the auxiliary verb "have" or "has" plus the past participle of the main verb. Examples of the present perfect in affirmative, negative, and interrogative forms are provided. The present perfect can be used with words like "yet," "just," "already," "for," and "since" to indicate when the action occurred or provide additional context. It is also commonly used with "ever" in questions to ask about experiences or things that have happened.