Well, you should define your terms. What do you mean by the term "oil" and define both "use" and "conserve".
Petroleum (Gr: Rock Oil) is a long chain hydrocarbon. It is a cheap, available source of "portable", storable, energy. It is being used to run all of the economies on this Global.
Should we conserve "oils" Well, we should conserve all resources and assets --- take only what you need and use it wisely.
So what is the rest of your homework question.