Install guest addition in Virtualbox

Guest addition improve the function and increase the function in between Virtualbox and guest OS.It is recommended to install guest addition on every guest OS.
These are the steps to install guest addition:

click devices and click install guest addition

open computer in the guest OS you will see a guest addition installer.Right click it and click open.

Enjoy.
Steps to install Virtualbox in Windows click here.
Steps to install Windows 7 in Virtualbox click here.