MacMost: System Preferences

Screen Time and Parental Controls In macOS Catalina
A new feature in macOS Catalina is the ability to track and restrict your app usage. You can use Screen Time for yourself, to attempt to limit your use, or as parent controls on a standard account on your Mac. You can also limit individual websites.
How To Change Your Mac User Account Picture
You see your Mac user account picture every time you log in to your Mac. You can customize this image easily in System Preferences with some default images, a photo, or any graphic you want. You can choose a photo and zoom in on one part of the image. You can create your own graphics or download an image to use.
Customizing Your Mac Login Screen
Most Mac users never take the time to customize their login screen. But there are several options there you will want to change to increase security or have the login screen better fit your needs. There is one very easy change that every user should make, to include a message on the login screen in case you lose your Mac and want to increase the chances that it will be returned to you.
How To Use Mac Hot Corners
Hot Corners are shortcuts that you can set so an action is performed when you move the cursor to one of the four corners of your screen. You can set these up in System Preferences if you know where to look. You can use them to instantly put your Mac to sleep, trigger Mission Control and other actions. You can also set them to work only with modifier keys. There is a trick to knowing which corners work in a multi-screen setup.
Removing Annoying Alerts By Setting Notification Alert Styles
Many apps will give you alerts that appear in the upper right corner of your Mac screen. You can set whether these alerts need you to click on them to dismiss, or they dismiss themselves automatically, or they don't appear at all. The settings for this are in System Preferences, under Notifications.
Quickly Switching Between Light and Dark Mode With NightOwl

Dark Mode in macOS Mojave is a great new feature, but Apple didn't give us a way to quickly switch between light and dark modes. The little donation-ware app NightOwl gives you that control in your menu bar. You can also set a keyboard shortcut, select apps to stay in light mode, and set specific times to switch between modes.

Multiple Screen Display Arrangement
If you are using more than one screen with your Mac, you can set where each screen is located relative to the others in your desktop's virtual space. You can choose which screen is the main one by dragging the menu bar representation to that screen. You can also adjust the rotation of your screens to use them vertically.
Privacy Preferences in macOS Mojave
Mojave changes how apps ask for privacy settings and gives you easier control of those settings. In System Preferences, Security & Privacy, Privacy, you can see all of the permissions that have been granted to apps and change them. However, for typical users it is often hard to determine why an app needs access to a specific type of information.
Using Dark Mode With macOS Mojave
A new feature of macOS Mojave is Dark Mode. This favors light text on a dark background instead of dark text on a light background in the system and standard apps. You can see the change in the menu bar, app toolbars and sidebars, and even the backgrounds of apps like Contacts, Calendar, Reminders, Notes, Mail and Maps. Not all apps will change, especially third-party apps. Document content and images will not change either, as they keep using the true color specified in the document. You can also change the accent color used in standard interface elements throughout macOS.
Using macOS Mojave Dynamic Desktops
The new Dynamic Desktop feature will change the image on your desktop depending on the time of day, or more accurately, the position of the sun. You can see this in action by manually adjusting your Mac's time. Apple includes two dynamic desktops with Mojave, but we may see more from Apple or third-parties at some point.
A Beginner's Guide to Mac Display Preferences
New Mac users may not have yet explored their display preferences. You can stick with the native resolution for your display or choose one that shows text and graphics larger or smaller. Which setting you use is a personal preference, and it is easy to switch between them when you need something different.
Using Smart Quotes
Smart quotes will allow you to type the same double and single quote keys on your keyboard but get different curly quotes in the correct direction in your text. It uses the character before the quote to determine which character to show. You can turn this feature off and on and use Undo to get straight quotes in individual cases.
Mac Privacy Preferences
You can view and change your Mac's privacy preferences in System Preferences, Security & Privacy. You can see which apps you have installed that requested access to things like Contacts, Photos, Location and other information. You can grant and revoke privacy permissions to these apps. You can also read more about what these apps can access.
Start Screen Saver With a Button
Normally, the screen saver starts after a period of inactivity, or when you use a Hot Corner. But you can also create a button in the Dock to start your screen saver with a click. This can be a handy way to quickly lock your Mac too.
Customizing the Menubar Clock
The clock that appears on the right side of your menubar can be customized to suit your needs. You can choose what to display and even switch to a compact analog clock. In System Preferences, you can set the time to be spoken aloud at regular intervals. There are many third-party apps in the App Store that offer even more options.
A Beginner's Guide to Desktop Backgrounds
The desktop background is the large image that appears behind everything you do on your Mac. You can change it in System Preferences. You can select from many provided images, choose a solid color, or use any of your own photos as a desktop background. You can also have the desktop background automatically change from a selection of images on a regular basis.
A Beginner's Guide to System Preferences
System Preferences is a small app that you can easily access where you can change some basic settings on your Mac. System Preferences is broken into categories, and then each category can be further broken down into subcategories with the names at the top. In macOS, unlike Settings in iOS, System Preferences is where you can find system settings, but not app preferences. Those are found in each individual app.
Using Night Shift on Your Mac
Night Shift is a new Sierra feature for recent Macs that shifts the colors on your screen to include less blue light. This can be useful for people using their Macs in the evening as more blue light may make it harder for some to get to sleep. Learn how to turn this feature on and off, and adjust it on your Mac.
Run a Screensaver as Your Desktop Background

A little-known trick will allow you to run your Mac's screensaver as a desktop background. You can use this to have an animated desktop, display useful information, or just for fun. It could be useful in situations where you have your Mac just playing music in a shared space and want something more interesting being shown than just a static image.

Set a Lock Screen Message
You can set a text message to appear on your Mac's lock screen. Use this to put contact information or instructions for someone who may find your lost MacBook. Change the message often to fit your situation.