getActionBar().setDisplayHomeAsUpEnabled(true);

onCreate()

onOptionsItemSelected

if(item.getItemId()==android.R.id.home){
                onBackPressed();
            }

<uses-sdk
        android:minSdkVersion="12"
        android:targetSdkVersion="18" />

<activity
            android:name="datepicker.DatePicker"
            android:label="@string/title_activity_date_picker" >
            <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.myfirstapp.MainActivity" />
        </activity>
        <activity
            android:name="gridviewcontext.TableItem"
            android:label="@string/title_activity_table_item" >
            <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.myfirstapp.MainActivity" />
        </activity>

android:parentActivityName="your_parent_activity"

<activity
        android:name="myomega.datepicker.DatePicker"
        android:label="@string/title_activity_display_message"
        android:parentActivityName="com.example.myfirstapp.MainActivity" >
        <!-- Parent activity meta-data to support 4.0 and lower -->
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.myfirstapp.MainActivity" />
    </activity>