Quotation marks are used for different things in texts. Sometimes they are used to mark actual quotations, things that people have said and written. Other times they are used to mark a word, such as this is “funny”. Some people also use them to
Single vs double quotes
There is not a right or wrong when it comes to using single (’) or double (") quotes. Different style guides say different things, so use whatever is suggested. In any case, the most important is being consistent.
You can combine single and double quotes if you have quotes within quotes: “This is my quote with ‘another quote’ within the quote”. Or the other way around. Again, be consistent.
Quotation marks in LaTeX
When writing in LaTeX, quotation marks should generally be typeset with different opening (``) and closing (’’) quotes. This ensures that they are typieset correctly.