Grounding wire in a bathroom vanity light bar
Making this with out grounding, or for you to do it at all with your level of electrical knowledge is a Bad idea. Vanity usually implies "in a bathroom", and that implies "near water". Outlets within (usually 1.5 meter, depending on your local electrical code) or a sink must have Ground Fault protection. Switches may not be within the same distance of a shower or sink. 

Even if your creation is not in a bathroom, extension cords are not intended for part of the permanent wiring of an appliance, and anything in which a light bulb can be replaced (thereby exposing the contacts) should be grounded and wired correctly (neutral to the shell, hot wire to the center contact, if a traditional screw in bulb). 

There are many certifications required for factory made electrical appliances before they may be turned loose upon the public. They exist for reasons. The fact that you even have to ask your questions indicates that you are creating a potentially unsafe device.  

Please at least put your project aside while you read up on basic electricity, electrical code, and safety.