Many people have taken the time and effort to create VirtualBox Appliances that are freely available to be used for many different reasons. Appliances are simply prebuilt virtual machines that we can import into our system.
To import an appliance simply choose File from the main VirtualBox window and click on Import Appliance to start the process.
Here we are presented with the file dialog window where we can choose which virtual machine to import. Click the folder icon to the right of the dialog window to browse to the virtual machine you wish to import.
After selecting your virtual machine appliance image click Next > to continue.
Here we are presented with additional information about the appliance we are importing. Click on Reinitialize the MAC address of all network cards to guarentee that the network cards of you VM are unique for each machine and click Import to finish.
Depending on your system's configuration and the size of the appliance it will take a few moments to import it. When it is finished you are taken back to the main window of VirtualBox where you can start your new virtual machine.