By default, the section number is shown in the course player, right in front of each section's title:
To hide these numbers, navigate to the Course player tab of your course, un-tick the Add numbers automatically in front of the sections' names option and click on Save.
Course Contents section
1. Visit the page of your school where you have added or will add a course section template.
2. Click on the Course Contents section to start editing it.
3. In the right-side panel disable the Numbering, under Section Appearance.