In electricity, there are three fundamental principals you need to grasp: current, voltage and resistance. Ohm's Law states that as long as resistance is kept constant, current and voltage is proportional. The fundamental definitions of V, I and R is crucial to learn in order to grasp the rest of the electricity chapter.
I-V Graphs is all about showing the relationship between potential difference and current. If a conductor obeys Ohm's Law, current is proportional to voltage and the graph will be a straight line through the origin. Non-ohmic conductors like the filament lamp has its curve flatten out due to electrical energy turning into heat energy and causing the metal to heat up - more vibrations cause electrons to move through the component more difficultly.