Use the future perfect tense to express an idea that something will end before another action in the future. Therefore, there are two future actions.

Future Perfect timeline

An action before another action (in the future)

1. He will have finished writing the letter (Action 1) by the time his father gets home. (Action 2)
2. We will have completed our work (Action 1) when you come. (Action 2)
3. I will have gone home (Action 1) when you come to my office at 5:00 PM. (Action 2)

As you can see, there are two actions – Action (1) and Action (2).  The sentence in Example #1, for instance, indicates that when his father gets home, the letter is already complete.

You have to use “will have” followed by the past participle verb form for the first action, while the second action uses the simple present verb form.

The past perfect tense expresses an action in the past that ended before another action in the past. In short, it is “the past in the past” action.

Past Perfect timeline

One action happens before another in the past

SCENARIO:
You’re now at the bus station but the bus isn’t there anymore, so you ask the porter. He informs you that the bus is gone. He says:

• The bus has just left when you arrived. – [The porter is saying it now.]

Later, you go home and tell this to your mom:

• Mom, the porter said that the bus had just left when I arrived.

Use “had” followed by the past participle form of the verb when you write a sentence in the past perfect tense.

When the present perfect is used, it indicates a completed action in the past before now. Duration and time expressions like “for two days”, “yesterday” and  “recently” are not important and not needed. What is important is that the action is done.

Present Perfect timeline

Completed actions in the past

1. They have eaten. – [ So they are not hungry now.]
2. I’ve peeled the oranges and (have) cut them for you. – [So it's easier for you to eat it.]
3. Sammy has returned the book to me. – [So I now have the book.]

Notice that there is an effect of the action. In Example #1 for instance, because “they have eaten”, the effect is “they are not hungry now”. The time they ate is not important. Use “has/have” followed by the past participle – not the simple past form – of the verb. That means, it is incorrect to say:

1. I have ate.
2. I ate already.

You may also add the word “already” to emphasize the action. Here are modifications to the examples above:

1. They have already eaten. 
2. I’ve already peeled the oranges and (have) cut them for you. 
3. Sammy has already returned the book to me. 

The past perfect continuous tense expresses two continuous actions in the past where one happens before the other (before now). Words that show duration like for, since and when are used. Look at the examples below:

Past Perfect Continuous timeline

One action before another in the past

1. You had been working in that company for a decade (Action 1) before you left. (Action 2)
2. When my husband came home, (Action 2) I had been cleaning the house the whole day. (Action 1)

In Example #1, you can clearly see two separate actions. Action (1) – working. Action (2) – you left
In Example #2, it’s the reverse. Action (1) – cleaning. Action (2) – exhausted

That means, the first / earlier action (Action 1) must contain the “had been“ and “- ing“ forms. The second / later action (Action 2) contains verb in the simple past form.

The present perfect continuous shows actions that occur in the past but continues up till now. In other words, there is a duration or a period of time. The words for, since and when are used to indicate duration.  Look at the examples given below:

Present Perfect Continuous timeline

Past actions till now

1. He has been staring at that girl for 5 minutes.
2. You’re late. We have been waiting since 10:00 AM.
3. Lately, I’ve been eating takeaways (or takeouts) as my parents are away.

Take note that in the present perfect continuous tense, you have to use the phrase “has/have been” followed a verb with “-ing“. In addition, notice that the word lately is also used as well to show duration.