...

The figure below explains why this second networking interface is necessary. The NAT interface is used only for accessing the internet. The host-only interface, in contrast, is used to allow access to your VM from your host computer (where the i2b2 Workbench is running).

6. Now add the Ubuntu ISO-file. Select the blue "Storage" entry in the VirtualBox main window. On the left side of the new window in the "Storage Tree" select the CD-icon labeled "Empty". On the right side, click on the blue CD icon and select "Choose a virtual CD/DVD disk file". Select the ubuntu-14.04-desktop-i386.iso which you have previously downloaded. The entry "IDE Secondary Master (CD/DVD): ubuntu-14.04-desktop-i386.iso" should now be listed in the VirtualBox main window under "Storage".