1. The simple present tense

* Use the simple present tense to talk about what regularly happens, what usually happens or what always happens.

E.g. Jane goes to college in the evening.
      You always seem worried.
      George usually reads his e-mails between 8:30 and 9:00.

2. The present continuous (or progressive) tense = verb to be + gerund

* Use the present continuous tense to describe something that is happening right now (at the moment of speaking.)

E.g. I'm talking to my best friend on the phone at the moment.
      The business executives are attending a meeting right now.
      Jerry is having lunch now.

3. The present perfect tense = have/has + past participle

* When we use the present perfect, there is a connection with the present:

E.g. I´ve lost my keys. (= I don´t have them now.)
      Ann has gone to London. (= She is in London or on her way there now.)

* We often use the present perfect to announce a recent happening.

E.g. I´ve lost my keys. Can you help me find them ?
      Did you hear about Ann ? She´s gone to London.

*We use the present perfect with this morning / this evening / today / this week / this semester, etc. when these periods are not finished at the time of speaking.

E.g. I'm very sleepy. I´ve had three cups of coffee today. Perhaps I´ll have more before the day is over.
      Has John had a vacation this year ?
      I haven´t seen Peter this afternoon, have you ?
      Karen´s hair was dirty. Now it is clean. She has washed it.
      A: Don´t forget to write the report.
      B: I´ve already written it.
      A: Why don´t you order a pizza ?
      B: I've already ordered it.

4. The present perfect continuous tense = have/has been + gerund

* The present perfect continuous often shows that an activity or state is unfinished. It started in the past and is still continuing.

E.g. I've been reading a novel for two weeks. (I'm still reading it.)
      Robert has been trying to save money since he was a teenager.
      (The emphasis is: He is still trying.)
      A: What have you been doing these days ?
      B: Well, I have been spending my free time in the countryside.
      A: Has Susan been working out lately ?
      B: Yes, she has been going to the gym three times a week.

5. Past progressive = was/were + gerund

A. It's used with the simple past to talk about an action that was interrupted by another action. Use the simple past tense for the interrupting action.

E.g. I was taking a course at the college when I met my wife.
      We were eating lunch when the phone rang.
      Where were you living when your son was born ?
      He was playing in the schoolyard when some older kid hit him.
      Mark was looking for a new job. But then he got a raise and decided to continue working at the company.

B. Use was or were going to to talk about future plans or expectations that you had in the past.

E.g. It was 1990. I was going to have a baby.

Notice that we often use was or were going to when things we expected to happen did not happen.

E.g. We were going to name the baby Mary, but when it turned out to be a boy we named him Paul instead.
       I was going to travel to the beach this weekend, but I changed my plans due to the bad  weather.

6. Used to

It refers to something that you regularly did in the past but don't do anymore.

E.g. I used to play tag with my friends when I was a child.
      She used to spend her vacations at her grandmother's house.
      They used to play with their neighbors when they were kids.

7. Past Perfect = (had + past participle)

It's used with the simple past tense to show which of the two events in the past happened first. The event in the past perfect happened before the event in the simple past tense.

E.g. When I arrived at the movie theater, the movie had already started, so I missed the first fifteen minutes.
       My house was very quiet when I got there. Everybody had gone to bed.
       Sally didn't come to the party last night. When I invited her, she told me she had already made plans.
       Charles was very nervous in his first driving lesson. He had never driven before.

8. Past Perfect Progressive = (had been + gerund)

A. It's used to talk about an action that was in progress before a specific time in the past.

E.g. It was 4:00 p.m. The athletes had been exercising since 1 p.m.
      Tina was very tired. She had been driving all night.

B. It's also used to express repeated actions in the past that happened before another event in the past.

E.g. The phone had been ringing for several minutes before he answered it.
      Jude had been watching TV for a long time when the lights went out.

9. Future Progressive = (will be/won't be + gerund)

A. It's used to talk about actions that will be in progress at a specific time in the future.

E.g. Professor Roberts will be attending a conference during the first week of August.
      At this time tomorrow I'll be driving to the countryside.

B. If the sentence has a time clause, use present, not future, in the time clause.

E.g. Sylvia will be working in the living-room while the maid cleans the office.
      I'll be answering the e-mails while my secretary finishes the report.

10. Future Perfect = (will have/won't have + past participle)

It's used to talk about a future action that will already be completed by a certain time in the future.

E.g. By the end of the year, she will have paid all her debts.
      Tom won't have finished the meeting by six o'clock.
      By 2010 Beth will have started college.

11. Future Perfect Progressive = (will have been/won't have been + gerund)

It's used to talk about and action that will still be in progress at a certain time in the future. The action may have already started or it may start sometime in the future.

E.g. My parents are going to move into their new apartment next month. By 2015, they will have been living there for six years.
       He started law school last year. By 2012, he will have been taking college for five years.
       By next year, Rose will have been working at "The New York Times" for seven years.