The virtual console is a browser-based secure VNC client.
It's using a HTML5 VNC Client, making it compatible with all recent browsers.
You can retrieve access anytime to your server and see what's happening on the screen.
Very useful if you want to install your own system with a Custom ISO.
The rescue mode will help you to recover from critical errors and to perform recovery tasks.
Your server will boot on the network and you'll be provided a SSH root access on a Debian live. From here, you'll be able to mount your virtual server disk and work on your system in order to bring it back to normally.
The rescue mode can be used too to backup your data or clone your system to a another server.