The English simple present tense expresses actions that are habitual or things that are always true. For example: I get up early every morning. The sun rises at dawn. The simple present requires only a subject and a verb, but the verb form changes for a third-person singular subject, such as "he," "she" or "it." When you use one of these subjects, the verb takes an "s" at the end: She loves her kitten. A noun referring to a third-person subject, such as "Mary," also takes the "s" ending: Mary loves her kitten.
The simple past tense describes actions that happened or were completed in the past. For example: I worked in the office until midnight last Thursday. The past tense of regular verbs ends in "ed" or "d," but some are irregular: They sat on the sofa. Past tense verbs stay the same for all subjects, including the third-person singular "he," "she" or "it": She sat very still in class yesterday. We often include time words such as "yesterday" with the past tense.
The English future tense expresses something that is yet to happen. It requires "will" or "shall" as a helping verb before the main verb, but the helping verb stays the same for all subjects. For example: We will overcome our problems sooner or later. He will take the train to Chicago. The future tense uses the base form of the main verb, which is the form listed first in a dictionary. Sometimes future sentences also use time words, such as "tomorrow": Tomorrow shall be a better day.
The present perfect tense describes an action that started in the past and is still going on or that still has an effect on the present. This tense requires three words -- a subject, a form of "have" as the auxiliary verb and the past participle of the main verb. The past participle is the third principal part of the verb and is normally listed third in dictionary entries: walk, walked, walked; see, saw, seen. "Walked" and "seen" are past participles. For the auxiliary verb, use "has" with a third-person singular subject and "have" with other subjects: I have seen many fires in my lifetime. He has walked 20 miles so far.
The past perfect tense describes an action that was completed in the past before some other action. This tense requires three words -- a subject, "had" as a helping verb and the past participle of the main verb. It's often used in combination with the simple past to show that one event happened before the other. For example: She paid off her car in 2010 (simple past). She had already paid off her car (past perfect) when she bought her house in 2011 (simple past). In the past perfect tense, the auxiliary verb "had" stays the same for all subjects.
The future perfect tense also shows sequence, describing a future event that will happen before some other future time or event. It requires four words -- a subject, "shall" or "will" as a helping verb, "have" as a second helping verb and past participle of the main verb. For example: I will have forgotten the dates before the history exam. Both helping verbs stay the same for all subjects: He will have retired before his son's wedding day.