Open the installer file and click Next on the welcome screen.
We'll install all the defaults, click Next.
Choose the options you'd like on your device then click Next.
During the install you'll have a brief moment where the network disconnects, hit Yes to acknowledge and proceed.
Some drives will need to be installed which will trigger User Account Control to ask you if that's ok, click Yes.
Click Finish, and that's it, VirtualBox is installed.
Double click on the downloaded disk image to mount the install drive. Double click on VirtualBox.pkg to start the install.
macOS will run a tool to make sure the software can be installed, click Allow.
We're not going to change any of the defaults here so click Install.
You'll be asked to authenticate, enter the username and password for an administrative account on your Mac.
After the install you'll get a message that a system extension is blocked, we need to allow it, click Open Security Preferences.
System Preferences will open with the Security & Privacy preference open. By default it's locked, click the lock icon in the lower left corner to unlock.
Enter the username and password of an account with administrative permissions on the Mac then click Unlock.
Once unlocked you'll be able to click the Allow button to allow the system extension.
A warning lets you know that this system extension won't work with a future version of macOS, click Ok.
The system extension requires a restart, click Restart, once it restarts you'll be able to access VirtualBox.