Web services are software modules connected via the internet
Web services are platform-independent software components for creating distributed applications. This means that web services are software components that run on various network computers and are connected to an application via the internet. Web services describe functionality and make it available via standard internet protocols. Subsystems are loosely coupled to applications through message exchanges.
Computers communicate with each other via web services
The web service itself is described in WSDL. It can access other systems via SOAP messages. Web services communicate between computers and not between computers and humans. Web services can upstream already existing software components (legacy systems) in order to integrate them. Instead of individual projects for the integration of specific components you achieve a single-platform independent approach. SOAP is the communication foundation of web services since it builds the basic structure as well as the processing instructions. SOAP is platform-independent and stands for Simple Object Access Protocol. The name proved to be unsuitable later, because you not only can you access objects, but also any XML structured content in principle.
SOAP messages can be transferred via HTTP or other internet protocols. Every SOAP message is an XML document. WSDL (web service description language) is used to describe the interface of a web service. This information will be used to access a web service.
You can find more information on web service on Wikipedia: https://en.wikipedia.org/wiki/Web_service