Sir could you please high light more about Cl graph and Cd graph how can I differenciate between this two graph

This graph from the FAA's, "Pilot's Handbook of Aeronautical Knowledge", may help you put it all together.

Note: The AoA for the best L/D ratio will depend on the characteristics of the wing. For this wing the L/D is a max at 6 degrees - not the normal 4 degrees in most training text books.

Carello's point is valid. Nobody ever said that the best lift/drag ratio always occurs at the same angle of attack for all aerofoils. 4° is often quoted as an example, but what matters is that each aerofoil has its own particular angle of attack for best lift/drag ratio that remains constant for that aerofoil. The same is true for stalling angle. 14 or 16° is often quoted as an example of the stalling angle but each aerofoil profile has its own stalling angle that applies to that aerofoil. Stalling angle varies quite a lot for individual aerofoils and it can be anywhere from about 15° to well over 22° for different aerofoil shapes.

However, any one aerofoil with a given setting for flap and/or other lift augmentation devices, will always stall at a particular angle of attack. The stall will occur whenever that angle of attack is applied no matter what the associated indicated airspeed may be.

Instructors should make this point clearer in briefings.