So I do not talk about basics now, but I'd like to talk about can i see it real world?
Yes we can. we can find it all the time. Some time it too hard to find it because it is too small action. But we can.
there are some example in here.
This is great pic for "Line of Action" As you can see, "Line of Action" make a dynamics. This is why animator consider it, we have to put the dynamics for your character.
And this other example is also good one. Two line related to each other and this make things so dynamics. Right arc try to get into left arc, in the other left arc try to away from right arc. We can feel lots of energy from this poses. This is a "Line of Action" in reality.
So all we have to do is find "Line of Action" in our life and vid ref and put it, that's it!
If we push "Line of Action" broadly, it is going to be super cartoony, put it with little push, it is realistic animation, instead of deadly puppet motion.