Installing Forge it's the same thing than installing Cauldron Pack. On Forge server you can only add mods, but with Cauldron, you can add mods and plugins in the same time.
So if you want to install Cauldron, follow all steps in the tutorial, just choose at the beginning in "Maintenance" and "Reinstall" panel Cauldron pack. Finally don't forget to install Forge client side into your computer.
If you don't know if your mod is compatible server side, you can check here.
You can only install "server-side" or "universal" mods. If you install a client mod, you'll have a crash and your server won't be start.