when to use ' ' and " " (Quotation mark usage)

[Nessie]

Hi,
Could you please tell me when to use ' ' and when " "?
(In my native language people just use " ", not ' ', so I don't know :) )

Thank you very much
Nessie.
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Sorry seems to be the hardest word...

[Atomos]

Hi,

Both ' ' (single quotation mark) and " " (double quotation mark) are used to set off speech, a quotation, a phrase or a word. Neither style – single or double – is an absolute rule, though double quotation marks are preferred in the United States, and both single and double quotation marks are used in the United Kingdom.

Source: http://en.wikipedia.org/wiki/Quotation_mark
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[Nessie]

Thanks a lot, Atomos.
I'm just curious because usually I just see Alan and Amy use single quotation marks.

By the way, In the link you gave there's something I don't understand very well:
'The convention in English is to give the first and each subsequent paragraph opening quotation marks, using closing quotation marks only for the final paragraph of the quotation.'
Eg:
“MY DEAR LIZZY,
“I wish you joy. If you love Mr. Darcy half as well as I do my dear Wickham, you must be very happy. It is a great comfort to have you so rich, and when you have nothing else to do, I hope you will think of us. I am sure Wickham would like a place at court very much, and I do not think we shall have quite money enough to live upon without some help. Any place would do, of about three or four hundred a year; but however, do not speak to Mr. Darcy about it, if you had rather not.
“Yours, etc.”
=> This paragraph is cited from the book 'Pride and Prejudice' of Jane Austen, and so I understand that there must be a quotation mark before "my dear Lizzy" and another after "etc", but I can't understand why there must be a quotation mark at the beginning of every paragraph. Does the same go for the original text?
By the way, is it compulsory that "MY DEAR LIZZY" be capitalised?

Many thanks
Nessie.
_________________
:(... something we never have again, I know... I guess I really really know.. :(

Sorry seems to be the hardest word...