Complex sentence: Just as he is about to give up, Charlie Brown sees a kite fall from the Kite-Eating Tree, and the string becomes entangled around his waist and sails away with him, quickly bringing him up to the bus's window.
Split into simpler sentences: Just as he is about to give up, Charlie Brown sees a kite fall from the Kite-Eating Tree. The kite string becomes entangled around his waist and sails away with him, quickly bringing him up to the bus's window.