Answers

2014-05-29T17:15:50+08:00
Do you mean past perfect tense and present perfect tense? :)
Had had, forms of past perfect, are used when we talk about an action that occurs before the other action, but both in the past.

Past perfect is formed with had + past participle, for example:
When I woke up in the morning, my sister had gone to school already. 
After I had eaten a breakfast, I washed my teeth.

Present perfect is formed with have + past participle. We use it when we talk about an action in unspecified past, for example:
There have been many typhoons in the Philippines. 
I have read this book many times.
I have had a nice conversation.

If you need to use time expressions, like yesterday, when I was a child, last yer etc. and you can't use present perfect, but past simple, for example: Yesterday I visited my friend.

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