The Revit SDK file has really useful files in order to get started, scripting with Revit API… This is a video found from autodesk that quickly presents the SDK file  http://download.autodesk.com/us/firstplugin/revit/exploring_the_revit_sdk_1044x828.html

You can download the Revit SDK file from Autodesk website

http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=2484975

as long as you have an activated Autodesk account…

So between these files the Revit API is included and also a pdf called “Revit 20xx API Developer Guide”  which has many useful details for a new programmer in Revit