Electricity can flow only if there is a complete circuit from the battery through wires to components and back to the battery again.
A capacitor stores electric charge. Polarised capacitors must be connected the correct way round. They usually have larger values, 1µF and greater. See above for uses.
Resistor A resistor restricts the flow of charge. Uses include limiting the current passing through an LED, and slowly charging a capacitor in a timing circuit. Some publications use the old resistor symbol
Microphone A transducer which converts sound to electrical energy.