Toughness and Endurance are your character's stats. Toughness determines your Attack points and Endurance determines your maximum Health points.
Attack signifies the amount of damage that you deal in fights with cadavers and other players.
Your maximum Health rate signifies the amount of damage that your character can sustain.
You can increase you Toughness and Endurance by collecting photo fragments, buying clothes and weapons, modifying your vehicle and upgrading objects in your home location and clan bunker. Also you can install Attack and Defense modules to your drone.
Regards, Nexters Support Team