PHP web service SOAP, wsdl file structure

I'm facing SOAP web services for the first time in PHP, I'm trying to understand the basics and the structure of the ".wsdl" file, I found so many examples and texts that I do not know how to rely on, for each example the structure changes, the tags change, in short, everything is different ...

I ask you a hand to choose a guide to learn how to create a web services in PHP and SOAP, excluding "nusoap and soap rest".

If there are more ways to proceed I would like to learn the best in terms of security.

Thank you very much.