This is a proper gearing-up scene, with the stormtroopers preparing for some (probably evil) mission. In the films before we've never seen much of the troopers outside of attacking our heroes. However, with Boyega playing a turn-coat there's ample opportunity to shed some light on how the Imperial rank and file actually operate. As for what said mission is, it's hard to make out with the light and smoke of the door opening, but this appears to be a night set action scene. This could either be where Boyega slips the net, or a platoon sent to track him down.