You'll encounter a control side mission about mid way through Act 1. There are two marked crates of supplies with a circle area around them. If a teammate (including Jack) is within the circle at the start of their turn, your supplies counter ticks up by one. You can see your progress at the top of the sreen and need to reach the flag icon to win the mission. Defend these positions, keeping someone in the circles in each turn and within a few turns you will complete the mission.