Need’ is used when you want to demand something that is absolutely necessary or something very urgent. ‘I need my medication’ ‘I need the papers immediately’  In both the above examples, the subjects cannot survive the particular context without the objects. ‘Want’ is used when you want to ask for something that is a desire or a wish. The speaker can use want to place a demand the listener might have to fulfill. ‘I want some cake’ ‘I want the entire document to be completed in an hour