Customise your Mac with System Preferences
You can change system settings to customise your Mac. For example, you can change the size and location of the Dock, choose a light or dark appearance, change the desktop picture, and more.
To change System Preferences on your Mac, click the System Preferences icon 
in the Dock or choose Apple menu 
> System Preferences.
Open System Preferences for me
Explore preferences
Options for your Mac are organised into preferences. For example, options you can set for Spotlight are located in Spotlight preferences.
Preferences appear as a grid of icons; the icons shown may vary depending on your Mac and the apps you have installed. Click an icon to open a preference pane and see the options.
By default, preferences are arranged in rows by category. To see them in alphabetical order, choose View > Organise Alphabetically.
Set options
Each preference pane contains options you can set. Most panes include a Help button 
to click for more information about the options.
Some panes are locked to protect your Mac, indicated by a closed lock icon 
at the bottom of the pane, and the options are dimmed. To unlock a pane so you can set options, click the lock icon, then enter the administrator password for your Mac.
Find options
If you don’t know where to find an option in System Preferences, use the search field at the top of the window. Options that match your search text are listed, and the preference panes where they’re located are highlighted.
If you see a red badge on the System Preferences icon in the Dock, you need to take one or more actions. For example, if you didn’t fully set up iCloud, the badge appears on the icon in the Dock; when you click the icon, the preferences are displayed so you can complete set-up.
To change options for an app, such as Mail or Safari, open the app, click the app’s name in the menu bar, then choose Preferences.