What should be the xml for Soap in PHP and how to process it?

Question

PHP

Good afternoon!
I understand with SOAP service and something is completely confused. I have a number of questions. I would be grateful for clarifications.
1. In what format are requests sent - xml or in the form of soap envelopes? That is, do you need to create an envelope yourself or SoapClient in php from xml makes an envelope.
2. How to validate an xml document. I know about xml schema, but I can't understand how it validates data in xml and returns an error in case of incorrect data.
3. How SoapServer parses data from xml. Suppose I need to call func($id) function where $id is in xml. Do I need to manually parse the file and insert the parameter into the function, or does SoapServer have some built-in tools?