I am a newbee in android developement...going through online tutorials..trying to see simple hello world on emulator but it says "Unfortunately demoapp(app name) has stopped.

Please help as its been 3 days I am trying to search the solution. when I am creating an android project, In package explorer with the demoapp(sample app name), it is also creating another folder appcompat_v7(Is it ok) as in tutorials I don't see that creating.

this is my manifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="...."
package="com.example.demoapp"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="20" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>