Complex sentence: This story begins as Ender Wiggin is made the commander of Dragon Army at Battle School, an institution designed to make young boys into military commanders to fight in the next interstellar war against an unspecified enemy.
Split into simpler sentences: This story begins as Ender is made the commander of Dragon Army at Battle School. The school is an institution designed to make young boys into military commanders to fight in the next interstellar war against an unspecified enemy.