有用 (yǒuyòng) is the everyday word for 'useful' — something that helps you do something. 有益 (yǒuyì) is more formal and means 'beneficial' (e.g., for health); 实用 (shíyòng) means 'practical' (functional, not just theoretical); 管用 (guǎnyòng) means 'effective, that works' in a specific situation.