System Settings is where nearly everything is configured. The search field at the top of its sidebar is the quickest way to find a setting whose location you don't know. Pane names below are the ones in current releases; if one has moved, search for it.
1Adjust Liquid Glass
Golden Gate refines the Liquid Glass design and adds a slider that controls how transparent or opaque the effect is. Look for it with the Appearance settings (System Settings > Appearance), or search for Liquid Glass in System Settings.
The same area lets you pick light or dark mode and the icon and widget style (default, dark, tinted or clear). If you find transparency hard to read, also try System Settings > Accessibility > Display > Reduce transparency and Increase contrast.
2Tidy the menu bar and Control Centre
Choose which status items appear in the menu bar, such as Wi-Fi, Bluetooth, battery percentage, Sound and Focus, in the Menu Bar or Control Centre settings (search for menu bar if you can't see them). Hold Command and drag menu bar icons to rearrange them, or drag one off the bar to remove it.
Whether the menu bar hides automatically, and whether it shows a background, are also set there.
3Dock, desktop and windows
In System Settings > Desktop & Dock you can set the Dock size and position, turn on automatic hiding, stop recent apps appearing in the Dock, and choose how windows tile (see the window tiling tutorial).
4Notifications and Focus
Go through System Settings > Notifications and turn off alerts from apps that don't need them. Set up a Focus (Do Not Disturb, Work, Sleep) in System Settings > Focus so notifications stay quiet when you want them to.
5Screen Time and parental controls
If a child uses the Mac, give them their own standard (not administrator) account, ideally a child account in Family Sharing. Then use System Settings > Screen Time to set downtime, app limits, content and privacy restrictions and communication limits. Settings for a child in your Family Sharing group can be managed from your own devices. See Apple Support for the latest options.