When we use OneNote Online, we can easily add a new page in a Note, just right click in the blank area in the page list area, then we can see the menu to Add a New Page:
Multiple pages are under a section, but some new users do not know where the option is for adding a new section. OneNote does not provide an easy way to add a new section like adding a new page.
How to Add a New Section in OneNode ?
We have to move mouse on the section colors blocks, check screenshot below: