

If there are more images available here (labelled debian-something-2, debian-something-3, etc.), they contain the extra packages that can be installed on a Debian system (as mentioned previously). Initially, you will only need to download and use the first image of a set (labelled as debian-something-1 to be able to start the Debian installer and set up Debian on your computer.

You need to download the first one debian-8.5.0-amd64-DVD-1.iso as described here : You can't boot from debian-8.5.0-amd64-DVD-3.iso it is not bootable.
