Should Hadiths and schools of thought be followed ?

Now if the Quran was given to us as complete and the word of God, then why do we have to follow hadith's and schools of thought of how to practise islam? I am a fairly new revert to islam and I just think of myself muslim and not a type of muslim, the quran does not say follow a school of thought or follow hadiths, its says follow the quran and do not make innovation. . . Thoughts?