You'll get rewards when playing in World Tour. Each challenge or tournament you play as a gold, silver and bronze reward. The rewards are stackable.
To get this achievement, simply play a challenge (which is just one game) on Easy (bronze medal). Win the match, and you'll unlock the item (usually a pair of socks in the earlier rounds of World Tour).
Now, go to your squad, and edit your player's apparel, Equip the unlocked item on him, and then go play another match with him. You do not need to win. As long as you finish a match with the item on him, the achievement will unlock at the end of the game.