Intent-filter In Manifest File To Enable The Open Button On Install

I am fairly new to Android Development and I have seen examples where this is put into the Manifest.xml file: <activity> element:

    <activity
        android:name=".<your activity name>"
        android:label="My App" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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