Supply Curve of a firm is basically Cost curve too , why so ?

The supply curve represents the amount of good / services sold. As the firm goes through the economies of scale, it's increase or decrease in production is highly associated with its pricing strategy. The more products means more demand means higher price and vise versa. 

I agree with Mr Ahmed answers, thanks for the invitation. ..

offcourse because if cost is more will be effect on price then sales

I apologize for the answer, I leave the answer to experts specialists in this field that's not my specialty field