In order to view the VAT on the overview page go to Overview -> VAT liability.  This displays your VAT liability on your overview page for the current period so you're not taken by surprise at the end of the VAT period.  Click on the amount shown to view the full report.  The "Download Calculations" button at the bottom of the VAT report page will show you how it was calculated.  You may want to see the VAT liability for another period, in which case go to Reports > General Reports > VAT Management and Reports.  More VAT options can be found by going to Settings -> VAT Settings.