Make sure you have the striker subclass selected, not defender. Once youve done that, look at your perks, if memory serves its the second perk down on the far right side, it replaces the armor buff during FoH. Once you have that all set up, in game start sprinting, after a few.seconds youll see a blueish aura in your peripheral vision on screen. This indicates your ready to charge, by pressing right bumper. Youll know youve used it because the attack zooms you out to thurd person view. Hope that helps, see you starside!