Debian Linux 6 was released in 2011 and is no longer supported. It is generally not recommended to use old and unsupported versions of operating systems, as they may have known vulnerabilities that have not been fixed.
If you still need to install libdvdcss2 on Debian Linux 6 for DVD decryption and playback, you can follow these steps:
/etc/apt/sources.list
file:deb http://www.deb-multimedia.org squeeze main non-free
wget http://www.deb-multimedia.org/pool/main/d/deb-multimedia-keyring/deb-multimedia-keyring_2016.8.1_all.deb sudo dpkg -i deb-multimedia-keyring_2016.8.1_all.deb
sudo apt-get update sudo apt-get install libdvdcss2
This will install libdvdcss2 and its dependencies.
Open your DVD player software. This can be a standalone DVD player application or a media player with DVD playback capabilities, such as VLC.
In the DVD player software, select the option to open a DVD from the DVD drive. This may be called "Open DVD," "Play DVD," or something similar.
The DVD should now start playing in the DVD player software. If you encounter any errors or issues, you may need to check that libdvdcss2 is properly installed and configured.