Can I install whatsapp web with a friend's phone so I can use it in my computer? (My phone is old :(

Most phone apps such as Whatsapp, LINE, and so on require that you use your own name, phone, and information. So if your friend has already signed up, then no. If not, and they ever want to in the future they will not be able to because you have, and even if they can that will disable yours in order for them to get it on their phone.