In "Gem for OneNote", click "Cooperation" tab -> "View" group -> "A4 Page" menu -> "Add A4 Letter Page" item.
Gem will insert an A4 frame, the A4 frame has a Genko with underlines.
Now, we can typing text on the underlines.
If you want to indent first line of paragraph, please input two Back Quote `. Detail:
Quickly indent the first line of paragraph in OneNote
If you want to insert another A4 page, just click "Add A4 Letter Page" menu item again. It will append an A4 frame at the end of the OneNote page.
If you want to print these A4 pages, please follow this article:
How to insert A4 page frames into OneNote page to limit for writing and printing?