This expression isn't exactly an idiom, but it has a particular meaning that words may not convey. It is the phrase, "what's the use."
First let me expalin that "use" used as a noun is pronounced differently than "use" used as a verb. As a noun the s is sounded like a hard s as in set or say or chase, but as a verb the s is sounded like z as in rose or rise.
The phrase means nearly the same as "what's the difference" but it includeds a feeling of hopelessness. For example, a father wants his son to study hard in college so he can get a good job after graduation, but the son knows there are no good jobs for a liberal arts major, so the son thinks, "what's the use" in studying hard if it won't help me get a job? It's like asking the question, "what good will come of it," all that effort for nothing.
So, "what' the use" is a common feeling among youth, especially those who get discouraged easily.
El parte de aprendiendo espanol para me mas dificil es distinguir una palabra de otra. Las palabras de un frasa se suenan como uno palabra larga. Tal vez porque hay tan mucho vocales.
Here are a couple more English idioms. He "gets my goat." This means he is very annoying.
Another one is: I sometimes go "whole hog." This means I sometimes go to extremes, or to use another idiom that means about the same: sometimes I "get carried away." Another idiom along the same line is: he "went bananas." This means he became very emotional, even hysterical, and lost his self control.
