Pages and sections in OneNote for Windows 10 are very similar to pages and sections in the OneNote for Windows Store app you might be used to from Windows 8.
What's the same
Working with pages and sections is virtually the same.
Adding a page—Select the + sign at the top of the Pages list on the left side of the screen.
Adding a section—Select the + sign to the left of the section tabs at the top of the screen.
Section groups are now listed under the notebook where they reside. When you select a section group, you'll see all the sections together on their own across the top of the screen.
Open a section group
To get to a section group, select the icon in the upper-left corner.
In the pane that appears, select the section group under the notebook where it resides.