How to 🐧 install flatpak

How to install flatpak
on Ubuntu Debian

sudo apt install flatpak
on Fedora

sudo dnf install flatpak (Usually pre-installed)
on Arch Linux

sudo pacman -S flatpak
on openSUSE

sudo zypper install flatpak
Add the Flathub Repository
This command is the same for all distributions. It tells Flatpak where to find the apps:

flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.f...
How to install GNOME applications via Flathub
flatpak install flathub org.gnome.Calendar