SOAP API Developer Guide

Introduction to SOAP API
Reference
Using the API with Salesforce Features
Implementation Considerations
Objects and SOAP API Calls and Headers for Apex
Outbound Messaging
Data Loading and Integration
Data Replication
Feature-Specific Considerations
Glossary
PDF

Objects and SOAP API Calls and Headers for Apex

These Salesforce Objects and SOAP API calls and headers are available by default for Apex. For information on all other SOAP API calls, including those that can be used to extend or implement any existing Apex IDEs, contact your Salesforce representative.

Apex class methods can be exposed as custom SOAP Web service calls. This allows an external application to invoke an Apex Web service to perform an action in Salesforce. Use the webservice keyword to define these methods. For more information, see Considerations for Using the webservice Keyword.

Any Apex code saved using SOAP API calls uses the same version of SOAP API as the endpoint of the request. For example, if you want to use SOAP API version 66.0 , use endpoint 66.0: 
1https://MyDomain.salesforce.com/services/Soap/s/66.0
These Salesforce objects are available for Apex.
Use these SOAP API calls to deploy your Apex.

All these calls take Apex code that contains the class or trigger, as well as the values for any fields that need to be set.

These SOAP headers are available in SOAP API calls for Apex.