Definitions of Tenses of Verbs -- American English
In grammar, tense means time. The tense of a verb indicates the time of the action or the time of the state of condition.

There are six tenses in English:
1. present tense     2. past tense    3. future tense     4. present perfect tense    5. past perfect tense     6. future perfect tense.

1. The present tense indicates the present time:    I know him.
2. The past tense indicates past time:           John was ill yesterday.
3. The future tense indicates future time:    I shall see you tomorrow.
4. The present perfect tense indicates an action that is completed at the time of speaking or writing:     I have called him twice today.
5. The past perfect tense indicates an action that was completed before some definite time in the past:
      At the meeting, I recognized a delegate whom I had met in Boston.
6. The future perfect tense indicates an action that will be completed at some definite time in the future.
7. The future perfect tense expresses the relation between two future times:
         ;  You will understand the subject of tense when you will have finished the class.
Verb Form Definitions
  1. The progressive form of the verb is the form that is used to indicate that the action is continuing at the time indicated by the tense:
    We have been planning to go to China.
  2. The emphatic form of the verb is used to give added emphasis to a statement:
    I did write that letter.