Once you have specified all the configurations, click the "Prepare to send mail" button.  This initiates a number of checks to ensure that configuration is valid. 

For each of the recipient types (HTML test, HTML live, TEXT test and TEXT live) a checkbox will be shown.  If the appropriate SQL Statement is valid and has retrieved records then the check box will be enabled for selection and show the number of matching records.  If there is a problem then the check box will disabled and the problem shown. 

If at least one HTML subscriber record is retrieved (Live or test) then the "Show Sample HTML" button is shown.  When clicked, a sample email for the first subscriber matched is displayed in your browser.  

Likewise, if at least one Text subscriber record is retrieved then the "Show Sample Text" button is shown, this launches a plain text email in Notepad.  

You will normally do a "test" user run first to ensure that everything is ok, then do the "live" run. 

If you have specified an appropriate log file on the Templates tab then the Maintain Log file check box will be enabled and ticked by default.