A super move is performed by pressing the Interact+Throw buttons at the same time. (LT+RT using default controls) Your special meter needs to be full in order to do your character's super move.
Meter is gained by attacking your opponent, doing special moves, and taking damage. Save your meter throughout the course of a match until your opponent is very low on health. Hit LT+RT at the same time to do your super and if it does enough damage to reduce your opponents health to 0, you will win the match and unlock the achievement.
Most supers will do 30-40% damage, so try to aim for at least that before using all your meter on a super. Also avoid doing moves that require super meter. Avoiding the Meter Burn button (RT) is usually all you need to do.
This can be done fairly easily in a singles fight on the lowest difficulty, or in a local match with a second controller if you're having trouble.