will and want

Will and want can both be used to talk about wishes, but they are rather different. Will is used mostly in ‘interpersonal’ ways, to express wishes that affect other people through orders, requests, offers, promises, etc. Want simply refers to people’s wishes – nothing more. Will is to do with actions, want is to do with thoughts. Compare:

• Will you open the window? (an order)
  Do you want to open the window? (a question about somebody’s wishes)
• She won’t tell anybody. (= She refuses to …)
  She doesn’t want to tell anybody. (= She prefers not to …)

Note that will cannot be used with a direct object.

• Do you want / Would you like an aspirin? (not Will you an aspirin?)

note

For a comparison between will and going to, (see here).