Could somebody explain when to use each of these
this is an apostrophe so I suppose it is used only in shorter versions of "it is" - "it's" or "they are" - "they're" and things like that. Nevertheless I would be grateful if someone explain this topic clearly.
For 1 and 3, I found this:
The American rule is that double quotation marks are the standard form, and single quotation marks (what the British call "inverted commas") are normally used only to enclose a quotation within a quotation.
The British usually, but not always, reverse this order, using single quotation marks first, and then double quotation marks to enclose quotations within quotations.
I am not a teacher, but I would like to share what I've been taught to do. I follow the, according to grammartips.homestead.com/quotationmarks.html, American rule. I do, however, use single quotation marks when I want to emphasize words or phrases in my handwritten essays (Normally I'd use italics, but that's when I write using the computer). :)