Would you show me a diagram of a series circuit?

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A simple series circuit can be built with a battery, a switch, and a light bulb. One end of the battery is connected to one end of the switch. The other end of the switch is connected to one end of the bulb. The other end of the bulb is connected to the other end of the battery.

If the switch is open, no current flows, and the bulb does not illuminate. If the switch is closed, current flows, and the bulb illuminates. By Ohm's law, the current through the bulb is proportional to the battery voltage and inversely proportional to the resistance of the bulb. Note, of course, that we are talking about hot resistance of the bulb, because cold resistance is an entirely different thing, due to the temperature coefficient of the bulb. Also, by Kirchoff's current law, the current at every point in this simple series circuit is the same and, by Kirchoff's voltage law, the voltage across the battery is the same as the voltage across the bulb.