There are many different electrical testing devices available, most of which are designed for professional use, although the proficient DIYer can use them. They are employed in various electrical applications, usually to ensure things are working as they should.
Detecting refers to finding (locating) something, whereas testing is finding out (measuring) something. However, the terms are often used interchangeably for tools which really only have one purpose. It is possible to get tools which both detect and test though, like a multimeter.
The purpose of voltage testers and detectors is to tell you something about the state of an electrical source and whether it is working safely. This can include whether there is live electricity or the current level of a circuit.For more information on what measurements can be taken from an electrical circuit see: How can electricity be detected and tested?
Voltage detectors and voltage testers are slightly different tools, however they are both used on AC electrical circuits to determine the presence of voltage. Voltage detectors can locate voltages without coming into contact with the electrical supply.For more information, see: What is a voltage detector?
Voltage testers are similar to voltage detectors but can sometimes be used on DC circuits. They are double probed devices which do need to come into contact with the electrical supply. This also allows them to test continuity.For more information, see: What is a voltage tester?
Electrical testing equipment
As these tools are electrical, it is difficult to specify exactly how to use them. Each model will be slightly different and may be used in slightly varying manners.
Most of these tools are generally for use by professionals who have electrical knowhow, but they have the potential to be used by DIYers who have a sound knowledge of electricity. It is important to read the instruction manual for each individual tool before beginning any project. You may also find it helpful to consult a professional electrician.