Android Sherlock ActionBar Up button

Question

Near Stream there is a small arrow that takes u to the previous activity when clicked

I want to make the same in my app, I used

  getSupportActionBar().setDisplayHomeAsUpEnabled(true);

do I need to use onOptionsItemSelected ?

The arrow is appearing, but nothing happens once clicked.

And I have two Items in my menu, they appear everywhere where I call OnCreateOptionsMenu

this is my item code where I want to to appear only in my last activity, How ?

      <item 
android:id="@+id/bAbout"
android:title="About"
android:showAsAction="always"/>