Resistance is like electrical friction.  It prevents the movement of electricity.  It is measured in ohms.

Series circuit--one path for the electricity.  This is the way some Christmas lights are wired.  When one stops working, none of them work.  Total resistance of a series is just the sum.

    Find the total resistance of a circuit with a 200 ohm, 500 ohm and 600 ohm resistor.
        200+500+600=1300ohms total resistance

Parallel circuit--more than one path.  This is the way...just about everything else is.  1/the total reistance (the total resistance ^--1) = 1/each resistor (each resistor ^--1) added together.

    The same resistors in a parallel circuit would be
        1/R = 1/200 ohms + 1/500 ohms + 1/600 ohms
        R = 115.385 ohms total resistance

A hybrid circuit has some resistors in series and some in parallel.  To calculate the total resistance of hybrid circuits, solve for the resistance of each parallel circuit first.  Then treat the parallel circuits like another resistor in series.
       Find the resistance of a circuit of 300 ohms and 500 ohms in parallel and 200 ohms, 300 ohms and 400 ohms in series.  1/R = 1/300 ohms + 1/500 ohms
                                            R = 187.5 ohms
            187.5 ohms +200 ohms + 300 ohms + 400 ohms = 1087.5 ohms resistance total