To do that, you should firstly choose virtual machine in the main menu of VirtualBox and click on the Settings button. Then click Storage tab in the Settings menu. After that, you will see an image of a disk and the word “Empty” under the Controller section. Click on Empty and choose the CD/DVD icon. Click Choose a virtual CD/DVD disk file and move to the ISO file that you are going to import to the virtual machine. Do as the prompted instruction to finish the process.