Electric Circuits:
A circuit is the path that electricity follows from where it begins (is generated) to where it is used. A complete circuit is a series of wires, or wire, that make a closed or complete path that the electricity can flow around. If we take a wire and loop it  so that it forms a continuous pathway, then we have the beginnings of a complete circuit. All we need is the source of power, the battery. Electric current is pushed through wires by a battery -  water is pushed through pipes by a pump.  Circuits need to be complete or they will not work!
The electrons (the electrical current) move counter-clockwise from the negative end of the battery to the positve end.
The negative (-ve) terminal of a battery pushes the negative electrons along the wire. The positive (+ve) terminal of a battery attracts the negative electrons along a wire.
Let's light up a small flashlight bulb!  Ready? First you will need a few things: a small bulb, a bulb holder, wire, masking tape and a small battery. Here is what to do: 1. Screw the tiny bulb into the tiny bulb holder
      2. Attach one piece of wire to each of the screws on the bulb holder. Leave the other ends of the wires free.
      3. Use the masking tape to attach the free ends of the wires to the battery–one wire to each end.
      4. Watch what happens when you complete the circuit

Series Circuits and Parallel Circuits
There is only one path in a series circuit for the current to travel and if there is a break in that path then the current stops. Whereas in a parallel circuit there is more than one way for the current to travel. That means that if one way is broken, the current just travels a different route. The current will only stop if all possible paths are broken.
Earlier I discussed with you resistance (last page). When there is resistance, currents travel slower. In the holiday season, you might hang colourful lights outside your home. If you have a long string of lights then you just might have a series circuit. With lots of lights, you will need more power if you want all the lights to shine brightly. Try making another circuit. This time attach 3 bulbs instead of just one. Try your circuit with a AA battery and then try it again using a D battery. The bulbs add resistance to your current flow.
Series Circuit
Parallel Circuit
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Disadvantages of Series Circuits
1. If one light in a series circuit fails, then all the lights in the circuit fail because the circuit has been broken.
2. The more lights there are in a series circuit, the greater the resistance in the circuit.
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BBC Electricity - Interactive - Very Good

Designing a Circuit - plus slide show
Electric Circuits - excellent