How to install a plugin on a server (Paper, Spigot, Purpur)
Plugins go on the server only — players don't need to download anything. They run on Paper, Spigot, Bukkit, Purpur, Folia; proxies use Velocity and BungeeCord.
Run a Paper server
Download Paper from papermc.io for your version and start it once: server folders appear, including plugins.
java -Xms2G -Xmx4G -jar paper.jar nogui
Download the plugin
On the plugin page choose the game version and your server software, then click Download.
Put the file into plugins
Stop the server and put the .jar into the server's plugins folder.
<server folder>/plugins
Start the server
The plugin creates its config folder on start. Check with the plugins command.
Where the .minecraft folder is
%appdata%\.minecraft~/Library/Application Support/minecraft~/.minecraftFAQ
Do plugins work on a Forge server?
Usually not: plugins are for Paper/Spigot, mods are for Forge/Fabric.