You need to make sure that Flatpak is installed in your Linux distro.
For installing Headlamp as a Flatpak, follow the instructions in its Flathub page .
For running it, just launch it as usually in your Linux desktop, or run:
flatpak run io.kinvolk.Headlamp
Headlamp can be used as an AppImage by downloading and running it directly.
To download, choose the latest AppImage file from the releases page . You can then run it by doing: