Follow these simple steps to start using Flatpak
A flatpak package is available in Debian Stretch and newer. To install it, run the following as root:
# apt install flatpak
For Debian Jessie, a flatpak package is available in the official backports repository.
If you are running GNOME, it is also a good idea to install the Flatpak plugin for GNOME Software. To do this, run:
# apt install gnome-software-plugin-flatpak
Flathub is the best place to get Flatpak apps. To enable it, run:
# flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
To complete setup, restart your system. Now all you have to do is install some apps!