I remember capacitors this way.  When I would put new points in a distributor, remember that.  There would be a cap. in there.  I asked what it was for or what it did.  I was told the coil puts out elect. all the time.  When the points are closed the elec. goes to the plugs, but for the split second they are open the elec. needs to go some place.  It goes into the cap.  It is a storage center. When the points close again the elec. flows out of the cap. and also from the coil.  Repeat. 

A resistor resist.  It slows down the amp flow.  Think of water flowing thorough a staw.  Squeeze the straw a little and the flow slows.  How hard you squeeze the straw is the size of the resistor.  Of course you need to size the resistor according to the amp size of the system.