Transformers are designed to increase or decrease the voltage coming from the electrical source. You can either step the voltage up or step it down. The voltage from the main lines to your domestic or commercial electrical lines depends on the country that you are in. If you already want to power up and safely use appliances and other electrical devices that does not have the same voltage input rating as your local electrical source, what you need is a transformer.
You have two types of transformers to choose from: the step up and the step-down transformer. Basically, the step-up transformer increases the voltage from 110V to 220V. The step-down transformer, on the other hand, decreases the voltage from 220v to 110V.
The type of transformer that you need to buy will depend on the voltage that your equipment needs. If the required input voltage of your machines is 220V but the supply is 110V, you have no choice but to use a step-up transformer. It is the same with step down transformer; if your equipment input voltage is 220V but you live in a country where the voltage source is 110V, you need to get a step-up transformer to be able to use your electrical devices and appliances.
If you look inside a transformer, you will see that it has three main parts: a core and two windings. The windings are different in a step up and a step-down transformer. In a step-down transformer, the winding connected to the AC current has more turns compared to the second winding. The induced electromotive force is smaller because of the lower number of turns. In a step-up transformer, it is the other way around. The first winding has fewer turns compared to the second winding. This difference causes the increase or decrease in voltage.