The 
Start Workbench is not really a workbench, it's just the page that is presented when you open FreeCAD with no document loaded.
From this interface you can create new files, jump to commonly used workbenches with the quick-start buttons ((v0.22) ), see useful information, jump to recently opened files, view examples, view the documentation, and get the latest news from the FreeCAD world. You can change how the Start Workbench behaves, or change the default workbench, in the Preferences Editor in the menu Edit → Preferences → Start.
⏵ documentation index > Start > Workbenches > Start Workbench/uk