In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
Q: The user rolls the ball with the thumb , fingers or the palm of the hand to move a cursor .
A: 
Users roll the ball to position the on-screen pointer , using their thumb , fingers , or commonly the palm of the hand while using the fingertips to press the mouse buttons .