The question mark is a fairly easy punctuation mark to use. It has one use, and one use alone. It goes at the end of a sentence which is a question. For example:
How many will be at the party?
you do not include a period when using a question mark. You also do not use a combination of question marks and exclamation marks in formal writing, though this is gaining acceptance in informal writing – particularly on the internet.
One thing to be careful of is to not include a question mark when it is not needed:
WRONG: I wonder how many people will come to the party?
While you are expressing a thought that seems to require an answer, you are doing so with a statement. This is the most common mistake made when using a question mark.