In English, only two tenses are marked in the verb alone, present (as in “he sings”) and past (as in “he sang”). Other English language tenses are marked by words called auxiliaries.
Simple Present: They walk
Present Perfect: They have walked
Simple Past: They walked
Past Perfect: They had walked
Future: They will walk
Future Perfect: They will have walked
The most common auxiliaries are “be,” “can,” “do,” “may,” “must,” “ought,” “shall,” “will,” “has,” “have,” and “had.”
The present perfect designates action which began in the past but which continues into the present.
1. June taught for ten years. (simple past)
2. June has taught for ten years. (present perfect)
The past perfect tense designates action completed in the past before another action.
1. Mike bred puppies and later sold them. (past)
2. Mike sold puppies that he had bred. (past perfect)
The future perfect tense designates action that will have been completed at a specified time in the future.
1. Saturday I will mow my lawn. (simple future)
2. By Saturday evening I will have mown my lawn. (future perfect)