SOAP provides a standard XML structure for sending and receiving information, much like SMTP. SOAP is often used in web services implementations to "hold" a message or data, and it often contains information in its header that describes where it is from, where it needs to go, how it needs to be handled, and so on. SOAP messages typically use HTTP as a transport layer, but you could use FTP, SMTP, JMS, or any other protocol.
In ColdFusion MX, consuming or publishing web services does not require you to be familiar with SOAP or to perform any SOAP operations. However, you should still make sure you read up on SOAP at the W3C web site (www.w3c.org).