Tenses demonstrate the time of an action through verb conjugation. There are three main tenses: present, past, and future. The present tense indicates current or habitual actions and has four forms: present indefinite, present progressive, present perfect, and present perfect progressive. The present indefinite tense uses the base verb form to denote actions that happen regularly or generally. It follows specific conjugation patterns based on subject. Some verbs like "have" and "know" are considered stative and use the simple form regardless of tense. Examples demonstrate the use of various tenses to indicate time.