I removed the Animation window at the bottom of the screen. How do I get it back? Thanks!

In the very corner of every area of the Blender UI, you will see a little icon with arrows pointing up and down. At the very bottom left of the screen, select this icon, and a menu will open Choose "Timeline" from the menu, and it will open the timeline in that area of the UI. Let me know if you need a screencap to assist.

Another way you can open to the default view if you have not changed or saved your view is at the very top next to Help you will see drop down arrow select default and that will bring you back to the default Blender screen view which includes the animation window just another way of doing it see screen shot below

I'm in the default view. Now that I've selected the Timeline, I not only have it back, it's taking up the whole screen, with what appears to be a history above it. Is there something in the Preferences I need to change? I made my own mess here. I found the "extra stuff" at the bottom distracting while I was just starting to learn the program, so I used "join area" to remove it. I'm used to programs with floating and pull-down menus everywhere, so I didn't think it would be so hard to find again.

On the bright side, I have had some progress with it. There are so many more tutorials out there for it now. I've made a cup of coffee and am doing the napkin-over-the-cup tutorial.

I had saved the startup file, so when I open a new scene I have everything again but the timeline. Do I need to use "Load Factory Settings"? Will that mess anything up? The working file was saved.

Load factory settings will reset Blender back to it's default and sometimes to be honest it is the simplest way to get back to default Blender screen. I do not know how many times just playing around exploring that I have made a mess of the UI and could not phantom how I got there and just want everything back to normal. Once you get more familiar with Blender you will come to a point where you will want to customize your UI it is simplest to click on the plus icon in the drop down menu you see in my screen shot it will duplicate the present UI you have then you can modify it rename first after you have hit the + icon modify the UI to your want then in File save start up file then the next time you start Blender you will be in that new UI look and you can always use the drop down menu to choose different UI looks for what you might be doing. Hope that makes sense

Thank you. Fortunately, it was a simple project and shouldn't take too long to redo...

Your welcome