A question mark is generally used at the end of a sentence to make the sentence a question, for example: ‘Did you finish that bottle of wine all by yourself?’
A question mark can really change the tone of a statement and can be used in writing dialogue to infer that someone speaks as though asking a question even if they are not (perhaps they lack confidence or simply do not speak “properly”), for example: ‘I think he’s right?’ Note the difference:
- You read the instructions first.
- You read the instructions first?
The first is a statement, quite definite in tone, and might be said as an observation. The second has a tone of ‘query’ to the statement, suggesting the person might not have done what they should have but the speaker does not want to overtly undermine them.
It is only ever used ONCE at the end of a sentence, regardless of how passionate one is asking the question! ‘???’ means the same as ‘?’ therefore it is unnecessary to use more than one question mark.
A question mark might also be used in combination with an exclamation mark to infer the question is being asked with a tone of excitement or disbelief, for example: ‘Who dared question my grammar?!’ There is a special mark used to describe this union, called an interrobang: ‽