When something fails to deliver a useful result, you can call it futile. Hopefully all the time you're spending studying vocabulary won't turn out to be futile!
Futile comes from the Latin futilis, which originally meant "leaky." Although we use futile to talk about more than buckets, the image of a leaky vessel is a good illustration of the adjective. Pouring water into a leaky bucket is futile. Your exercise program will be futile if you don't stop chowing down on chocolate. Futile is fancier than its synonym useless. Other synonyms are fruitless or vain. The i can be either short (FYOO-t'l) or long (FYOO-tile).