A virtual phone number is a real number on a real mobile network that you rent for a short time instead of buying a SIM card. Any text message sent to it appears in your account within seconds.
Websites and apps send a one-time code to a phone number to confirm that a real person is behind a new account. When you rent a number, you enter it on the sign-up form, wait for the code to arrive in your dashboard, and type it back in.
Each number is used for a single activation. If no message arrives before the timer runs out, the order is cancelled and the money returns to your balance automatically.