Before we start, make sure your server version supports plugins. Some common server versions which support plugins are Bukkit, Spigot, Paper Spigot, Sponge Forge.
Here’s a guide on how to change your server version.
- Download your desired plugin (common plugin websites are https://spigotmc.org/resources and https://dev.bukkit.org)
- Open your server’s files (here’s a guide on how to do this)
- Navigate to the /plugins/ folder
- Upload your plugin
- Reload (not recommended) or restart (recommended) your server
If the plugin doesn’t load make sure you installed the correct version and followed the installation guide provided by the author.