While writting the mac address changer we have use the ifconfig command to know kali’s ip nad mac address, taking notes while watching the course will be very helpful. In windows you can use ipconfig command, look at the ipv4 and you’ll know which is your target machine’s ip.
And in a real scenario it’s not that easy to know which is the ip of the target machine, you’ll need to capture some traffic and analyze it, it might give you a clue to identify the target. Also the mac addresses can give you an idea because most of them have specific numbers assigned to vendors, I mean you can know if the connected device is apple, windows, huwaei, tp-link, etc. Check this website: https://macaddress.io/ (obviously this won’t work for virtual machines as the mac address they have is fake)
Hope it helps!