Got it. I'm posting this for the benefit of any other rank newbs who are going through the "Getting Started" steps on the soapUI site.
1. In Proxy Settings, set proxy to localhost:8088. Not sure if this is completely necessary but that's the way I'm set up right now.
2. For the sample project provided with soapUI: Start the SampleServiceSoapBinding MockService if it isn't already started,
leave it running (this is where my troubles began - I had stopped the service), then set the Request 1 URL (top of the Request 1 screen) to
http://127.0.0.1:8088/mockSampleServiceSoapBinding.
3. Run the request. You should get a session ID as a response.
