1, about Kali Linux
Kali Linux is a Debian-based Linux distribution that is designed for digital forensics and penetration testing. Maintained and financed by Offensive Security Ltd.  The first Mati Aharoni and Devon Kearns by offensive security were completed by rewriting backtrack, a Linux distribution that they had previously written for forensic purposes.
Kali Linux comes preloaded with many penetration testing software, including NMAP (Port scanner), Wireshark (Packet Analyzer), John the Ripper (password cracker), and Aircrack-ng (one should software for penetration testing of wireless LANs).  Users can run Kali Linux from hard disk, Live CD or Live USB. Metasploit's Metasploit Framework supports Kali Linux,metasploit a set of tools for developing and executing exploit code for remote hosts.
Excerpt from: Http://zh.wikipedia.org/wiki/Kali_Linux
2, download iso& installation
Download size is 3G, larger than the best use of Baidu pan offline download.
Install VirtualBox and map the ISO file directly.
Set the root password and log in with the root account.
Select the disk format, the default is the line.
Then the default installation, waiting for the installation to complete the reboot.
3, enter the system
System Login interface. Log in with the root account. is a derivative version of Debian.
After entering the system, a lot of penetration testing software is installed by default.
Kali Linux is a derivative version of Debian. There is a more convenient graphical interface, then continue to research penetration testing tools.
Penetration Testing (1): Virtualbox Installing Kali Linux