When your health reaches Zero, you enter a "Worn Out" state. You are impervious to enemies but you can only crawl in this state. If you crawl away from enemies, you can meditate and regain your health, but when you meditate, enemies can then attack you. If your too close to enemy when you meditate, then can attack you, and you will then die.
The enemy you look directly at, you will auto target. You can use this to quickly move the camera and in turn change targets to help you keep control of fighting multiple enemies.
When you upgrade your skills, they get added to a panel of skills. the panel is arranged like this,
|Tab - Jump||Left Click||Right Click||F|
Skills and the Skill bar will change depending on the situation. If you have a move that works at a distance, the skill button will light up indicating it can be used from that distance. The Skill bar also changes when you grapple or get on top of an enemy.