To begin, launch the VirtualBox application (located in /Applications). Once the application loads, click on the New button in the toolbar to start setting up and installing a new virtual machine.

The Create New Virtual Machine wizard will then pop up, walking you through the process of creating a new virtual machine. To continue, click on the Continue button.

This screen will allow you to specify a save name for the virtual machine you are creating as well as specify the type of virtual machine that you're creating. Be sure to select the appropriate operating system and Version from the drop-down menus. When you are finished, click Continue.

This screen lets you specify how much RAM you would like to allocate to your new virtual machine. We will go with the recommended base memory size that VirtualBox recommends, but if you have more RAM on your Mac to spare, feel free to increase the size. When you are finished, click Continue.

On this screen, a VirtualBox will recommend a virtual hard drive size. If this is your first time creating a new virtual disk, ensure that "Boot Hard Disk" is checked and that "Create new hard disk" is selected, then click the Continue button.

The Create New Virtual Disk Wizard will appear, allowing you to create a new hard drive file to store your virtual machine on. Click Continue.

The next screen will allow you to select the type of disk file you would like to create. Dynamically expanding storage means that as your virtual machine needs more space, additional storage will be automatically allocated. Fixed-size storage does not expand automatically. For this virtual machine, we'll select "Dynamically expanding storage." Click Continue when you're done.

On this next screen, type a name for the new virtual disk. Next, select the initial size for the disk drive. We'll go with the recommended settings here. When you're done, click on the Continue button.

The last screen of the new disk wizard will give you a summary of the newly created disk file. Click the Done button to continue setting up the virtual machine.

After finishing the new disk wizard, you will be done setting up the virtual machine. The "Create New Virtual Machine" wizard will give you a summary of the newly created virtual machine. To continue, click the Done button.

Next, insert your operating system install disk into your Mac and click on the Start button in the VirtualBox Manager window.

The VirtualBox First Run Wizard will appear. Using this wizard, you will select the drive that contains your OS install disk. Click Continue.

On the Select Installation Media screen, your Optical Drive (CD/DVD) will be selected by default. Since this is the location of our installation media, we'll go with that and click Continue.

After clicking Continue, you will be presented with the Summary Screen for the First Run Wizard. To continue with the OS install, click the Done button.

VirtualBox will then begin loading the media in the optical drive of your Mac. Assuming you have set everything up correctly, you will be able to complete the operating system installation as you normally would. When you have finished the operating system install, go to the next step in this how to in order to install the VirtualBox Guest Additions software.

After your guest operating system has been installed in the VirtualBox virtual machine environment, click on Devices > Install Guest Additions (or press Command + D). This will open up an installer inside of the virtual machine that will install relevant system files to make the virtual machine run better on your Mac. After completing this installation, your virtual machine set up will be complete.