have present perfect

Hello !
Nowdays, I have been studying the expression 'have present perfect'. present perfect tense.
There was not the expression 'have p.p', so I was confused at that expression. 

I am going to write down for some examples.
Could you correcting correct these, please :)

1. I have visited in Singapore for one time.
2. I have lived in Seoul ever since 1987. <--- PERFECT!
3. She has read Harry Poter for two months. <--- This means she is STILL reading it.
4. My parents have eaten breakfast everyday every day. <--- This is okay, but a little strange to say.
A better sentence is "My parents have eaten toast for breakfast every day." [My parents have eaten (WRITE FOOD NAME HERE) for breakfast every day.]
5. He has written a diary since for three years ago. <-- In present perfect tense, it started in the past and continues today (a habit). If you say since/ago... as these two words are slightly different in meaning, would mean that he does still do this or, even, that he has stopped! 

*I hope you can understand me. Let me know if you have any other questions!* 

Thank you !!! You're very kind. But I have a question. She has read Harry Poter for two months. -> Why it means she is still reading?? If I make it means still reading, I wrote it 'She has been reading Harry Poter for two months' ??

1.) She has read Harry Potter for two months. --> This means that she has been [1] reading Harry Potter, [2] finished the book, and for some reason [3] started reading it again (for two months.) Do you know the English expression "to do something off and on again for ___ months/years"? It is like that. Because you said "has READ" (read is in past tense) it means that: yes, she may have finished the book once (in two months) but she chose to STILL read it (again) in those two months. 

I hope that helps. I know it is confusing. Sometimes, even native English speakers sturggle with the Present Perfect! 

To fix this sentence, just take out the "two months."
She has read Harry Potter. -> (She did this in the past, but we need to NOW, because it affects us now.)

If you REALLY want to say how long AGO she read it: She read Harry Potter two months ago. (Just use past tense "read" with # + months/days/years + ago.)

2.)  She has been reading Harry Potter for two months. --> You are correct! This is the right way to say she is still reading. (because read + -ing)

HOWEVER, sometimes even Native speakers do not catch the tense and when we hear "has + read/reading" (because it is in present perfect) we just think it is still happening. In conversation it basically means this activity is still happening today. 

So in Sentence 1, she chooses to still read it. In Sentence 2, she never finished but is still trying to finish the book.