Turn on and off Arduino

Dear Sir/Madam,

I use the Arduino Uno and program via the USB cable.

This is the first time I use Arduino, what should I do between I program two new projects, should I need to unplug the USB cable or any button I should press or program I should upload to the board, how can I turn it off except unplugging the cable?

Best regards,

Kelvin.

(deleted)

I usually just unplug the cable to stop the program - that is provided you also have no other power source for the Arduino