During the prologue, or the "Trial of Evil" you will progress through a tutorial on some of the more basic functions of the game.
After you get the initial 2 minions and also dodge the fire balls with the RS, youll come to a point where you can free hit a pillar for minion cubes. Just keep hitting it and spamming which ever button becomes available. Eventually I had enough minions to trigger the achievement.
The achievement is also trackable on the achievements tab of Xbox