There are small square boxes that show up at the bottom of my email. They say inbox and have sign. I do not want them showing up

You are seeing the Mail Shelf - each thumbnail representing an open Mail window/view. Where multiple Mail windows are open, a simple tap of a thumbnail will instantly switch to that view.

The iPadOS multitasking environment permits you to run multiple instances/windows of the same App, such as Mail - with each window, perhaps having a different open inbox or draft mail message.

This article from Appleinsider has a useful explanation of this feature along with many of the updates to multitasking:

https://appleinsider.com/articles/21/08/12/how-to-master-multitasking-on-ipad-and-ipad-pro-in-ipados-15

The iPad User Guide is also a rich source of frequently overlooked information. The Guide is available both online using a web browser (such as Safari), or as an Apple Books download:

iPad User Guide - Apple Support

https://books.apple.com/book/id1567104892

The Shelf is an integral element of iPadOS multitasking. Unlike iPadOS14 and earlier versions, multi-tasking (including split-screen, slide-over views and the Shelf) cannot be disabled from settings.