Photos will not open and screenshots won't save

Right-- I think you're going to need to get hands-on help by someone who can see your computer and operate the keyboard. The best thing would be to find someone near you to help-- maybe at an Apple Store, if that's possible.

When you say "my photos would open without an app" are you referring to QuickLook, where you click on a picture and hit the spacebar to see a preview of the picture? All files, including picture files, must be viewed with a app. In Quicklook the app is Finder.

If you want to be able to double click on a picture and have it open in a particular app, you can do this: Select a picture on your desktop and type command-i (⌘-i) to get the info window. Towards the bottom it has a field for

"Open with:" and it tells the default app for that kind of file. My default for jpegs is the app GraphicConverter, but the usual default is Preview. You can pick any app that will work, and you can click "Change All" to make it open all files of that sort with the same app.

You didn't mention how you take a screenshot.

Take a screenshot - Apple Support

In some cases the screenshot goes to the clipboard (my favorite.) In other cases the screenshot appears for editing. In others it goes to a folder of your choice. you can change the default location of saved screenshots from the Options menu in the Screenshot app. What, exactly, have you done?

A jpg file is not a picture-- it is a bunch of 1s and 0s that must have a program to turn those 1s and 0s into something recognizable. QuickLook gives a temporary view using the Finder app. Double clicking on a jpg file is usually set to open an app that will show the picture and provide viewing and editing options. I showed a picture earlier that showed the app in the info window.

If you click on a jpg file and type command-i (⌘-i), then an Information Window opens. It looks like this:

This is for a movie, and the arrow points to "Open With:" and the field says "Quicktime Player app"

When I double click on this file, or any file like this, it opens in the app Quicktime Player and pays the movie.

Here is part of an info window like I showed earlier:

As I said earlier, "My default for jpegs is the app GraphicConverter, but the usual default is Preview. You can pick any app that will work, and you can click "Change All" to make it open all files of that sort with the same app."

So, when you check the Get Info for a picture, what does it say for "Open with?"

So, when you checked the Get Info window for a picture, what did it say for "Open with?"

Shift Command-3 produces a tiny editable preview in the lower right corner-- do you get that?

The "little list of save options at the bottom" occurs with the screenshot app-- are you using that?