I have this sentence:
The world knows how you feel.
You can change the world with it: It knows how you feel.
So it is right, because if you use The world know how you feel. and then you replace with it: It know how you feel.
But what about this one:
Let the world know how you feel
or
Let the world knows how you feel.
Should it be let it knows or let it know? Why, is that a third person?