Live DVDs (or live environments) are one of the neatest features of Linux. You can try any distribution that offers a live image without installing, and there are distributions designed specifically to run from CDs/DVDs/USBs.
A live environment has many advantages. It needs no installation, so I can run on any compatible hardware. this means that if you can access a PC (and are able to reboot it), you can have your own operating system running on it, regardless of what was previously installed. Once you finish and log off, there will be no trace of your usage, everything will run as normal, like nothing ever happened.
Using a Linux distribution that way can have many uses. Some use it for privacy-conscious computing in possible hostile environments (there is a distro for that too), or it can be used to rescue broken computers, extract data from failed systems, forensic analysis that leaves the inspected system unchanged and interact, or just evaluating a certain distribution.
Debian live environments allow you to run a specific spin of Debian Linux, with a single Desktop Environment and a useful set of basic software installed. Live DVDs offer a great way to familiarise yourself with Linux (or Debian specifically), test out different Desktops before you make up your mind what to install, and can even be used to prepare your hard drives for installation, if you want to dual-boot with another system, like Microsoft Windows.
When you head over to the download page, you will find many different files, with long, obscure names. The names of the images end with the included Desktop Environment (before the ".iso" part, such as
will come with the KDE Plasma Desktop, while
means it ships with the Cinnamon Desktop for the live environment, etc. You can later install a different DE if you like, but the live system will run with the specified DE.
After having burnt it to a DVD (live images are all DVD sized), or copied it onto a sufficiently large USB drive as detailed in the previous chapter, you can just restart your computer, and choose to boot from the removable media. To achieve this, you will need or press a Function key (often F10 or F12), and select the drive from the list.
What key you need to press and whether you need to enable booting from removable media in BIOS/EFI is specific to your system. If you are unsure, you should check your computer's manual, or the vendor's online documentation.
If you are greeted with the Debian GRUB screen (more on that later), you know you were successful.
Just press enter and you should soon find yourself in the Live environment, ready to explore Debian.
From there you can use the system as normal, but any modifications you make, will be lost. It is possible to create a writable storage in a USB to be used with the system to keep your data on, but that is beyond the scope of this manual.
You will not need to download another installer image. If you like what you see, you will b able to install Debian straight from the Live DVD, by selecting either "Graphical Debian Installer", or "Debian Installer" from the initial GRUB menu.