According to our theory of solar system formation, why do all the planets orbit the sun in the same direction and in nearly the same plane?

The planets orbit the Sun because the gravity of the Sun attracts the planets. The lightest (planets) always orbit around the heaviest (Sun).

The planets move in the same plane because they were born in the same plane of matter. The Solar System was originally a large mass of rotating gas and dust, so the planets are all created with the same matter.

Explanation: I hope I have helped you. Good luck.