Generally, a quotation is enclosed in double quotation-marks and any interior quotations are enclosed in single quotation-marks: "Is this what they mean by 'overthinking things'?" he asked.

My thoughts are the first ‘. ‘ could be in a paragraph but between this marks reference to table or photograph on page xxxx The second are speech marks and should be used only for speech . Ie he went to the station tick office and asked for a return ticket to London. He bought ticket and then mutter under his breath “that was expensive”.