EAS is the speed that you would need in the ISA at sea level to get the same dynamic pressure as you get at your TAS in your actual air mass. It is not an actual velocity.
Correct.
You need to know it because dynamic pressure is what makes the airplane fly.
Wrong. Dynamic pressure is a theoretical concept, a convenient reference pressure for calculating aerodynamic coefficients. The real pressures generated in compressible air make the airplane fly.