What is the function of fear and how do you learn fear?

I found out that this gave much more meaning when we changed perspective of the question into:

How to learn courage and become more fearless?

Which in the answer would be that courage is not a LACK of fear, but merely facing your fear to realize that there is nothing to be afraid of: thus the funtion of fear is just that.

So the function of fear seems to be some kind of guide. I.e facing death or other situations that are outside of your comfort zone to realize that they are nothing to worry about.