Hi Chooka,
There are a few different ways that you can install BOINC.
One way would be to open a terminal window and enter the following ...
sudo apt install boinc-client boinc-manager
But you don't have to manually type these sorts of commands.
You can just copy and paste the command from your browser into the terminal window, then hit Enter.
The Virtual machine I downloaded already had Firefox installed (which is the same browser that I use in Windows), so I can browse the web from within my VM and copy and paste text from the browser into the terminal window.
You can also copy and paste things from Windows as well.
In VirtualBox, if you right-click on your virtual machine, then click "Settings", there are various different things you can set.
If you click "General", then go to the "Advanced" tab, there is a dropdown box for "Shared Clipboard".
I have this set to "Bidirectional" which lets me copy and paste between Windows & Linux or vice-versa.
To paste text into the terminal window, just right-click anywhere in the window and select "Paste".
Another way that I have been installing software is with "Synaptic Package Manager".
It lists heaps of software packages along with descriptions and lets you install or uninstall them without having to enter any commands.
You can just click on the software you want to install and select "Mark for installation", then click the "Apply" button at the top of the screen.
I installed Synaptic with the following command ...
sudo apt install synaptic
Since installing Synaptic I have mostly been using this to install software rather than commands in the terminal.
In Synaptic you can browse through the various categories of software, or do a search for a specific program.
If you search for boinc you will find a package called boinc (the description is "metapackage for the BOINC client and the manager").
Just right-click on it and select "Mark for Installation", then click the "Apply" button at the top of the screen.
A popup appears that says "Mark additional required changes?" - click "Mark".
Click "Apply" again.
Note:You can also get newer versions of BOINC from the following PPA (Personal Package Archive):
https://launchpad.net/~costamagnagianfranco/+archive/ubuntu/boinc(I can describe how to do this if you want - I just didn't want to complicate things too much)