Unlike REST, which is an architectural style, SOAP is a protocol. It is perhaps reasonable to compare working with SOAP to importing a .NET assembly (DLL) to work with the types inside. As a result, a SOAP client is much more strongly tied to a server than is the case with a REST interface.
SOAP uses XML to exchange information between client and server.
SOAP-based web APIs are, these days, quite rare.
The New-WebServiceProxy command is used to connect a Web Services Description Language (WSDL) document. The document is written in XML and can be viewed in a browser.
The command accesses a service anonymously by default. If the current user should be passed on, the UseDefaultCredential parameter should be used. If explicit credentials are required, the Credential parameter can be used.
The following example creates a proxy, which is used to access a web service that exposes information about Mendeleev's periodic table of the elements:
$periodicTable= New-WebServiceProxy...
