If you are unfamiliar with what VirtualBox, Linux, and Kali Linux are, then head on over to the "where to start" directory where I have added some great links to videos and readings on those topics. I'll even give you a link right to it, here: Let's Learn

Before you get started

Before you get started, I recommend downloading a download manager. It is not necessary but can be helpful. You can download a popular and free one called Free Download Manager. I mean, that name could not be better. If you ever google "hey I want a free download manger", boom that's the first thing that is going to pop up. If you're not sure why you should get it, maybe this article will help.
Why You Should use a Download Manager

I also recommend you create a folder in your home directory called VirtualBox images and store all of these images that you are downloading in there. You can also create folders for each of the machines within VirtualBox images. The two Kali machines and the Parrot OS machine can go in a folder called OVA files. The SEEDLabs Ubuntu machines can go in a folder called VMDK files and the iso image can go in a folder called ISO Images. Stay organized, it only makes life easier!

VirtualBox

If you don't already have VirtualBox, go ahead and download it. We all use it, so if you have any trouble with it, don't be afraid to ask for help! I recommend also downloading the extension pack after your VirtualBox installation has finished. You will find it right under the download you just clicked on. It will be called "Oracle VM VirtualBox Extension Pack". Download it and then double-click it. It will open VirtualBox; then just hit install.
VirtualBox

With whatever virtual machine you decide to download, after running the instructed update and upgrade commands, make sure you take a snapshot! Doing so will save the state of the machine. You should title it "fresh install"; for the description, you will put something along the lines of "Just installed this vm and ran the instructed update commands". Now, if anything happens to your machine, you can always restore this snapshot and run it like you just installed it. It is recommended that you create snapshots before doing anything big. I always take a snapshot after downloading certain tools because some of them can be a pain to download and install.