https://www.gamespot.com/articles/destiny-2-how-leveling-up-and-power-numbers-work/1100-6453135/

Destiny 2's progression system is relatively straightforward, especially compared to the first Destiny before. But if you're new to the series, you'd be mistaken in thinking that experience points are the only thing you need to worry about on your journey. So here's a breakdown of how it works.