Go to the Downloads page and choose the "Windows (Installer.exe)" download option. When the program is downloaded, run it, and the Installation Guide will walk you through the process.
Go to Floodlight's website and choose the "macOS (.zip)" download option. When the file is downloaded, open it. Drag the extracted application to your "Applications" folder.
The first time you open Floodlight, you should see a message that it is an application downloaded from the internet. Click "open". You will only see this message once.
First, check your distro's Software app. If Flatpak is preinstalled, Floodlight might already be listed, and you'll just have to click "Install".
Otherwise, follow Flatpak's setup guide to install Flatpak for your distro. Then, go to Floodlight's website and choose the "Linux (Flatpak)" download option. Opening the file should launch your Software app, which will have a button to install Floodlight.
If that doesn't work, launch Terminal and run the following command:
flatpak install flathub io.gitlab.floodlight.Presenter
This will install Floodlight.