In this example, the volume icon is added. Other icons are available and can be found in their respective System Preferences category. Examples include Bluetooth, Wi-Fi, and Fast User Switching.

1) Open System Preferences.

2) Click Sound.

3) At the bottom of the window, ensure that the box labeled "Show Sound in menu bar" is checked.

4) There may be additional options to control when the icon appears. For instance, for the sound icon there is a drop-down menu to choose either "when active" or "always". Choose your desired preference.

OUTCOME

The desired icon will appear in your Mac's menu bar (top right corner of the screen).