Kali Linux is a distro based on Debian that is designed for pentesters, it comes in with a large number of pentesting tools pre installed and ready to use.
In this video you will learn how to install it as a virtual machine inside Virtual Box in under 2 minutes.
Resources:
Za1d's Blog 
[…] I explained how to install Kali Linux as a virtual machine inside Virtual Box, in today tutorial you will learn how to install Kali Linux using the ISO image, […]