How does my character level up?

You character can’t level up though you can increase your maximum health and increase the efficiency of your medkit, increasing your chance of survival. These two can be improved by leveling up the Infirmary and Healing Garden facilities respectively.

In addition to that, you’ll unlock more abilities and tools through perks. Spend Perk Points to permanently unlock new abilities such as takedowns against high rank enemies, additional weapon slots, increased melee damage, longer breathing, etc, and tools such as the repair torch, grappling hook, fishing rod, and more. Some perks like increasing your medkit, throwables, or ammo capacity can be purchased several times, stacking their effect.