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
Voltmeter Measures voltage. The proper name for voltage is potential difference but voltage is more widely used.
A capacitor stores electric charge. It can be used with a resistor in a timing circuit, for smoothing a supply (it provides a reservoir of charge) and can be used as a filter (blocking DC signals but passing AC signals). Unpolarised capacitors usually have small values, less than 1µF.
Preset variable resistor A preset is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than standard variable resistors so they are sometimes used in projects to reduce the cost.