Dear All,
If you come across any problem while you try to connect your usb wi-fi card to your Kali Linux you may follow the steps below:
1) Try to define your device within other USB ports rather than your current one within Virtualbox such as 1.0, usb 2.0 or usb 3.0.
2) Try to unplug usb wi-fi card from your computer and plug it in after Kali Linux starts only.
3) Try to plug your usb wi-fi card to different physical USB ports on your physical computer.
4) Open Kali Linux settings from Virtualbox when Kali Linux is closed. Open Processor tab from System section. Make sure you make Enable PAE/NX option ticked.
5) Run this command from terminal and restart Kali Linux
sudo apt-get install linux-image-$(uname -r|sed 's,[^-]*-[^-]*-,,') linux-headers-$(uname -r|sed 's,[^-]*-[^-]*-,,') broadcom-sta-dkms
6) If none of these works you may search for Kali Linux drivers for your usb wi-fi card and find your documentation online to install them on your Kali Linux. This is not necessary for most of the usb wi-fi cards however there might be some cases that you need to install this.
7) If nothing above works you should search for your specific usb wi-fi card model and chipset with google such as "Ralink 3070 Kali Linux connection" in order to find simple solutions. If you come across with comments stating your device does not work with Kali then you are going to refund it and find another one that works unfortunately.