MacOS provides a variety of options to set up a screensaver -- a term that, in this case, means any image that hides your desktop when you are not using your PC. Some of the options provided use collages of preset images, some use the images you provide, others use animations of geometric shapes, while some use animations with words or sentences.
1) Click the apple icon on the Menu bar.
2) Select System Preferences in the drop-down menu.
3) In the System Preferences window, select Desktop & Screen Saver.
4) In the window that opens, go to the Screen Saver tab.
5) In the left pane, select a screensaver style.
6) In the right pane, open the Source drop-down list.
7) In the Source list, select the source of the screensaver images. In this example, I have selected the Photo Library. You can select from macOS presets or your own photos.
8) Click Choose to complete the process.