Simplify the following text for a Grade 4 native English-speaking person.
Original: In the simplest play , the string is initially wound on the spool by hand ; the yo-yo is then thrown downwards so that it first descends unwinding the string , then ( by inertia ) climbs back winding it up ; and finally the yo-yo is grabbed , ready to be thrown again .
Simplified: In the simplest play , the string is wound on the spool by hand . The yo-yo is then thrown downwards , so that it goes down and unwinds the string .