Answer:
What does everyone know how to open but not how to close?
The sharp slim blade, that cuts the wind.
I am the red tongue of the earth, that buries cities.
We are all around, yet to us you are half blind. Sunlight makes us invisible, and difficult to find.
What can you fold but not crease?
They are many and one, they wave and they drum, Used to cover a state, they go with you everywhere.