Ultimately an action sequence document is nothing more than an XML document. The XML Source Tab is where to go if you wish to view or edit the raw XML. Keep in mind that manually manipulating the XML is not encouraged.
If you have a Pentaho BI Server running, the test tab can be used to test your action sequence against the running server. Simply enter the URL to the running Pentaho server and select "Run". Your action sequence will be submitted to the server for execution and the results will be displayed within the tab.