I am confused with the usage of "have had" and "had had". When can I use them?

"have" and "had" too...

Ex: I had written this: (about something that happened a few months ago)

I have achieved a rank which gets me admitted...

An expert and a genius corrected this as:

I had achieved a rank that got me admitted...

I could have asked that expert, but I didn't find that person online whenever I came online... I wish that person could answer me!!

I am confused with the usage of "have had" and "had had". When can I use them?

"have" and "had" too....

Ex: I had written this: (about something that happened a few months ago)

I have achieved a rank which gets me admitted...

An expert and a genius corrected this as:

I had achieved a rank that got me admitted...

I could have asked that expert, but I didn't find that person online whenever I came online...I wish that person could answer me!!!
I'm good with grammar tenses (am an expert on a grammar site). Please tell me the entire sentence and sentences before and after.

Hey its you whom I was talking about...

Wondergirl, are you there?

I was eating lunch. I'm here now.

I just want to know when to use those words.

Today I came through a sentence:

He has had thin time too.

Why can't it be:

He had had thin time too.

* a thin time
I missed "a" in both the sentences

I just want to know when to use those words.

Today i came through a sentence:

He has had thin time too.

Why can't it be:

He had had thin time too.
I need the paragraph it's in.

Rohini : Raj appears quite prosperous. He is quite lucky.

Lasya : He has had a thin time too. Days were when he found it difficult to meet the expenses of his children's education.

I was learning some english expressions and I found it as an example.

Rohini : Raj appears quite prosperous. He is quite lucky. [present tense]

Lasya : He has had a thin time too. [past tense, conditional, action has occurred over a long period of time] Days were when he found it difficult to meet the expenses of his children's education. [past tense]

Doesn't "had had" fit into that sentence? It represents past tense.

Doesn't "had had" fit into that? It represents past tense.

Doesn't "had had" fit into that? It represents past tense.
No, it is the past before the past. It is not simple past tense, but more past than past.

Lasya : He has had a thin time too. [past tense, conditional, action has occurred over a long period of time] Days were when he found it difficult to meet the expenses of his children's education. [past tense]

Lasya: He had had a thin time too. [past perfect tense, action has ended] Days were when he found it difficult to meet the expenses of his children's education. [past tense]

Okay what about "have" and "had"?

I've studied many articles about him..

I think it should start with "I had" but I don't know the reason. Because it is past (more past)?
If it had occurred recently, then it has to be "I have", isn't it? Am I right?

Sorry, am I annoying you?

What is actually "conditional" ?

I have to write my application essays, SAT essay and TOEFL essay. So, I am incredibly worried particularly about these phrases and words.

Okay what about "have" and "had"?

I've studied many articles about him..

I think it should start with "I had" but I don't know the reason. because it is past (more past)?
If it had occurred recently, then it has to be "I have", isn't it? Am i right?
Right.

I have studied many articles about him. (it means an action that started in the past and continues now, or has the possibility of continuing now.)

I had studied many articles about him. (action is finished)

I had had (past before the past) many boyfriends before I got married (the past). The past must be mentioned before you can tell about the past past.

Oh okay... now I understood what is past before past exactly.

Then what is conditional?

Then what is conditional?
Conditional meaning action has occurred over a long period.