How to make my layout able to scroll down?

Just wrap all that inside a ScrollView:

<?xml version="1.0" encoding="utf-8"?>
<ScrollView
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
    <!-- Here you put the rest of your current view-->
</ScrollView>

As David Hedlund said, ScrollView can contain just one item… so if you had something like this:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
    <!-- bla bla bla-->
</LinearLayout>

You must change it to:

<?xml version="1.0" encoding="utf-8"?>
<ScrollView
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
    <LinearLayout
      android:layout_width="fill_parent"
      android:layout_height="fill_parent">
        <!-- bla bla bla-->
    </LinearLayout>
</ScrollView>