The action bar Sherlock is a third-party library which include the basic action bar library of Android and it make the action bar compatible with older versions.
Since the tutorial of the official web page is not so extensive, here is a list of the tutorials which are quite good.
Vogella - Using the Android action bar(ActionBar) - Tutorial
AndroCode - Introducción a ActionBarSherlock (Spanish)
Xavi Rigau - HowTo: ActionBarSherlock + MapFragemnt + ListFragment