In electronics, an item is either a conductor, an insulator or a semiconductor. A conductor flows electricity freely, as in the case of a copper wire. An insulator, like the plastic coating on a wire, stops electricity completely. A semiconductor is halfway between an insulator and a conductor. It allows some flow but blocks, or resists, some flow. A resistor is a small semiconductor with two wire leads. Resistors absorb electricity and are used to limit voltage flow.
A capacitor is made by placing two metal plates close together with a thin insulator between them. Wire leads are connected to the plates. A voltage is fed into the two leads. A capacitor stores a charge until a saturation point is reached. When that happens, the capacitor releases all its charge through the leads. An unqualified person should never reach into the open cabinet of electronic circuitry. Even if the power is removed, all the capacitors are storing charges. if a person touches a capacitor, it discharges through the person, causing a shock and possible electrocution.
In a series RC configuration, one lead of a resistor is connected to a power supply, The other lead is connected to one lead of a capacitor. The output lead of the capacitor is connected to the other side of the power supply. In a parallel configuration, one lead of a resistor is wrapped around one lead of the capacitor. The other leads are wrapped around each other. One set of leads are connected to one side of a power supply, with the other set of leads connected to the other side of the power supply.
When power is applied, the capacitor starts to charge and discharge. The output of the circuit is taken from the resistor by placing an output lead on the lead of the resistor. By the action of the circuit, a sawtooth wave is produced. The voltage rises little by little as the capacitor is charging. When the capacitor "dumps" its entire charge, the voltage at the output drops to zero. Sawtooth waves have their place in electronics. For example, a radio transmitter has to produce an output frequency. An RC circuit produces part of the output frequency wave.