To change the order of Sections and Lessons within the Overview, go to the Course Overview and hover over the Section or Lesson that you want to move. Click and hold the move icon, then drag the individual Section or Lesson to the place you'd like it to be.
From the Course Overview, you can also move a Lesson into an existing Section. To do this, hover over the Lesson, click and hold the move icon, then drag the Lesson into the Section where you'd like to move it.
You can create a new Section from a group of Lessons by hovering over the Lessons, filling the bulk select icons, and clicking the "Create Section" button.
To change the order of Lessons in a Section, go to the Section and hover over the Lesson you want to move. Click and hold the move icon, then drag the Lesson to the place you'd like it to be.