You first develope your whole layout. then put that layout inside a scrollview. Remember that a scrollview always takes only one layout and cannot take more then that. so remember to design your page in a manner that there is only one outer most layout and then put that whole layout inside ScrollView.
If you want only part of your page then put the elements that you want to scroll inside a layout and then put that layout inside a scrollView.
<ScrollView>
<LinearLayout>
//the whole page
</LinearLayout>
</ScrollView>
<LinearLayout>
//some elements
<ScrollView>
<LinearLayout>
//elements to be scrolled
</LinearLayout>
</ScrollView>
</LinearLayout>