iPad 8- ios 16 mini photos along bottom of screen

You have encountered the iPadOS “Shelf” - this being a feature of the revised iPadOS multitasking environment. 

iPadOS permits you to have multiple App windows - “instances” of the same App - each window being self contained. The shelf, when triggered, shows a thumbnail of each running instance of an App.

For example, if you have three running instances of Safari, each with its own set of open tabs, you will see three thumbnails corresponding to each running instance of Safari - plus a button to open a new instance/window of Safari. Simply tapping a thumbnail will switch directly to that running instance of Safari. Each App - such as Mail, Safari, Notes, Calendar, etc. - has its own corresponding shelf.

Individual App windows can be closed directly from the Shelf; just swipe the unwanted thumbnail off the top of the screen. Note however, that Multitasking and associated Shelf functions cannot be disabled.

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

You mean the apps on the dock on the bottom of the screen? Those are the same as any other apps, however, they stay on the dock for easy selection. You can bring the dock up from any screen on any app making it even easier to access those apps. If you want to put apps in the dock, you can simply drag them from where they are located on your Home Screen to the dock and they will stay there and be easily accessed from anywhere. If you want them off, you drag them off and put them back on the Home Screen where you want them and then you can control what apps are there or not.