Mission Pass

What actually gives you start to level up the tiers in the mission pass?

You need to earn Mission Stars through completing ARKS Missions to unlock Tiers. You get 5 Mission Stars for completing your Daily ARKS Missions, 5 for completing your Weekly ARKS Missions, and a large amount weekly from the Tier ARKS Missions, with some Tier Missions giving up to 9 Mission Stars.

ya what AndrlCh said. If you need more info about how it work. here a video that may help https://youtu.be/qGbpo9pihcU