Your car's ignition system produces the high voltage electricity needed to start the engine. Its ignition coil amplifies the low current from the battery into tens of thousands of volts. The distributor then transfers these high-volt pulses to the spark plugs at the cylinders. But to transmit current to the spark plugs at the right time, the distributor needs a rotating part called the distributor rotor.
Mounted on the distributor shaft, the ignition rotor spins inside the distributor cap as fast as the camshaft or at half the speed of the crankshaft. As it rotates, the rotor arm transmits the electric current to a number of points in the distributor cap. Because there's really no contact between the rotor and these points, the electrical spark only "jumps" from the tip of the rotor to the cap terminals, all the way to the spark plugs. Given this crucial function, the distributor rotor must always be in tiptop condition. A rusty or worn-out rotor will just create misfires in your ignition system.
The success of the ignition process heavily depends on the rotor. So if you notice that your rotor is acting up, it's about time to have it inspected and probably replaced. It's ideal to replace the rotor together with the distributor cap for ensured performance. And lest you risk your ignition system, get only original equipment replacement parts from trustworthy stores.