Your OSX System Preferences Explained
These are your Mac's System Preferences. They can do a lot. So, as an exercise, I'm going to go through each of them, one a day, and show you what they do. For starters, you can find them in your Apple menu, very top left of your screen.
System Preferences #1 - General
This one's mostly about appearance, such as highlight colour and size of sidebar icons. My suggestion, as always, is to open it up and see what each option can do. You can't ruin anything. The one that matters to me the most is the option for automatic scroll bars. After upgrading to a new OS, you may be dismayed that your scrollbars have disappeared due to the default, 'automatically based on location'. First thing I do is switch that option to 'always'. I just don't like to hover in hopes that my scrollbars will appear. You ight also want to select, 'ask to keep changes when closing a document', too.
System Preferences #2 - Desktop and Screensaver
This is where you choose your desktop picture, whether it's from Apple's default folders or your own Photos library. You can choose to rotate through a selection of your photos on a schedule of seconds, minutes or days. If you don't want your slideshow to include your entire Photos library, you can create an album of your top 10, 50 or 200 etc photos, and select it as your target folder.
There are screensaver options on the second page, though screensaver are not as crucial as they were when we used old cathode ray tube (CRT) monitors