I have installed Kali on Virtualbox but the problem arises with the wifi adapter.
From what I understand, it is necessary to have an external USB wifi adapter with injection capabilities, in order to do any kind of wifi hacking.
Hey, be polite!
The video is not useless based on what you said there ^ you seemed that you couldn't make the bridging the videos shows what you just did. You didn't specified any of the needed information such us " I made the bridging via the VM but Kali won't recognise the interface via airmon-ng." except if you can find the previous sentence somewhere on your first post. Next time be more specific if you would like to avoid missunderstandings.
Now probably Kali won't detect your hardware (wifi adapter) properly, cause it is lacking the specific drivers.
Here is some fast steps that will make it happen.
Run this on your terminal as root:
lspci -nn | grep Network;
Get the name of the card and then google this:
Debian official drivers for <paste the results you got from the previous command(the adapters name)>
This will give you the package's name for the wanted hardware, then either install it via apt suite(suggested) like this:
apt-get install <package name>
Or if for some reason the previous one won't work download the package from the page and install it like this:
dpkg -i <path to the package>
Give some feedback, if it worked or not.