Adapters are devices that take attributes from one system and transform them to become usable by a different system that is in itself incompatible with the system that provides the attributes. The most common examples of adapters include units that convert AC current to DC current, the adapters that make special plug configurations, such as the plugs intended for being used in the US, compatible with systems that use different configurations, such as the power outlets used in Europe and USB adapters that convert USB data signals to and from other communication protocols.
Adapters are usually small devices that are easy to use. They usually feature intuitive configurations, meaning that the connectors they are equipped with can be used only one way. Adapters being used for connecting to otherwise incompatible systems, they usually feature one connector for each of the two systems. The two connectors on the adapter usually look very different, what’s more, they are usually distinguished with rings of the color that you will find on the plug belonging to its respective system, so you cannot make a mistake when plugging the connectors. The adapter will start working when both systems are powered, up and running, the transformation process taking place either automatically or after turning on the adapter.
You can find out more about adapters and cable/plug connectivity at https://iec.net/.