The description just says "gain an advantage--" does that mean the character succeeds on the roll, check, or saving throw?
Starting at 1st level, you can manipulate the forces of chance and chaos to gain advantage >on one attack roll, ability check, or saving throw. Once you do so, you must finish a long >rest before you can use this feature again. Any time before you regain the use of this feature, the DM can have you roll on the Wild >Magic Surge table immediately after you cast a sorcerer spell of 1st level or higher. You >then regain the use of this feature.