To install a Minecraft plugin: stop your server, drop the .jar file into the /plugins folder, then restart. The plugin loads automatically. Works on Spigot, Paper, Bukkit and most hosts.
Download the plugin's .jar file, drop it into your server's plugins folder, then restart the server (or run /reload). On hosted panels like Aternos, Apex or BisectHosting, upload the .jar through the file manager instead. The plugin loads automatically. Confirm it works by running its commands or checking the console for a startup line.
In your server's /plugins folder, alongside the other plugins, then restart the server.
Make sure the plugin version matches your server version, the .jar is in /plugins, and read the startup console for the exact error.