Video Guide!
We need to reach level 15 to unlock the Bear Ally ability from the Ranger skill tree, luckily there are no other prerequisites, so this can even be our first unlocked Ranger ability.
Then, we just need to find an enemy Bear and call in our friendly Bear using the radial menu. It is important to note that the two bears actually have to interact during the fight. Our Bear friend has some short attack range and his AI is a bit silly, so we may need to kite the enemy bear around a bit before they finally hit each other.