To make a single picture your desktop. Simply save it somewhere you can find it on your computer. Then right click on it and select "Set as desktop background" and voila. Depending on the size and resolution, some pictures will look better then others as your desktop.
Now, how to make a group of pictures that you choose alternate as your desktop background. First save all the picture you like in a folder. Then right-click directly on the desktop. Select "Personalize", then "Desktop Background" at the bottom of that window. It will give you something that looks like this....
Now all you have to do is find your folder location, then put a check mark on the picture, or pictures you want as your desktop image. Notice at the bottom where you can modify the position, and the amount of time it will take to switch to the next one.
If you like some of the pictures I post and haven't already saved the ones you like. The easiest way to find them again is to click on a specific label like Wallpaper, Redheads or Gun Porn as examples, and find your favs a lot faster. Have fun... ;-)
Oh, and out of curiosity, let me know by clicking "reactions" or commenting if this was helpful in some way... I hope it is :-)