If you have a small screen (like a MacBook Air), you might not want a permanent clock taking up space. You can "Stack" widgets.
: Drag the desired clock widget directly onto your desktop or click the (+) button to add it to your Notification Centre. Finalise : Click Done to save your layout. Customising Your Clock How To Add Clock Widget On Mac mac clock widget
The built-in Clock app provides several designs, including analog, digital, and world clocks. If you have a small screen (like a