How start learning soapui

Learning SoapUI can be very easy or very difficult depending on your current level of skills and your expectations from SoapUI. If you are wanting to just 'use' SoapUI as a basic smoke test style tool than it should be rather simple to manually edit the test steps on an as-needed basis. If your wanting the test cases to dynamically update themselves from a datasource than it can become extremely difficult.

I have a post on SQA.StackExchange that I think is a decent introduction to SoapUI and some of the different things you should look into learning in order to become more adept with SoapUI. Depending on your desired skill level will depend on what you need to learn though.