The PDF documents available in the _documentation/guides folder or /Developer/docs/guides folders include a Soap Developer’s Guide and a Web Services Developer’s guide that might get you started.
You can also find tons of information in Google on this topic.
Focus your efforts on Soap Document/Literal (aka Soap-MSG) style as Soap-RPC is not compliant with the Web Services Interoperability (WS-I) basic profile 1.0 or later.
IS 7.x still support SoapRPC, but you should not use it if interoperability between consumers and providers using different tools or soap stacks is a goal.
Read the ‘sticky’ posts in the SOA Service Development forum for more examples.