To download and install applications from Flathub, you will need to install Flatpak (if you haven't already) and then add the repository in one of two ways:
Using Flathub in GNOME Software
If you are on Arch, Debian Stretch (or later), Endless OS, Fedora 25 (or later), Mageia 6 (or later), or OpenSUSE Tumbleweed, you can download the repository file and use GNOME Software to install it.
Using Flathub on the Command Line
From the command line, run:
$ flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
You can then browse and install applications in the normal manner. See the Flatpak command line tutorial for more information on this.
If you develop a Linux application and would like to make it available via Flathub, we would appreciate your contribution. Follow the instructions at submission guidelines to submit your app.
Security or legal issues can be reported to the Flathub maintainers.