From PSU: “The Division 2 offers eight different skills to use during combat. These improve your arsenal and grant you new abilities to help you take down the deadly enemy factions. You can equip two of these at a time and they are activated using the shoulder buttons. Each skill also has multiple different variants, allowing you to truly customise your loadout to your playstyle.”
Source: N4G PC The Division 2 – Best Skills To Unlock First