Prerequisite: You must first change your server software to a type that supports your goal. See Changing Server Software.

For Plugins: Use Paper or Purpur.
For Mods: Use Forge or Fabric.

Installing Plugins (Paper/Purpur)

Plugins run entirely on the server. Players do not need to install anything on their end.

Step 1: Download the Plugin

Download the .jar file from a reputable source like SpigotMC or Modrinth. Ensure the plugin version matches your server version.

Step 2: Upload to Server

Go to the Files tab in your panel.
Open the plugins folder.
Click Upload and select your downloaded .jar file.

Step 3: Restart

Restart your server to load the new plugin. Check the console for a startup message confirming it loaded successfully.

Installing Mods (Forge/Fabric)

Mods change the game code and usually render new blocks or items. Players must install the exact same mods on their computer to join.

Step 1: Download Mods

Get mods from CurseForge or Modrinth.

Crucial Check: The mod must match your specific Mod Loader (Forge vs Fabric) and Minecraft Version (e.g., 1.20.1).

Step 2: Upload to Server

Go to the Files tab.
Open the mods folder (created automatically after you start a Forge/Fabric server once).
Upload the mod .jar files here.

Step 3: Client Installation

Remember to send the mod files to your players. They need to install the same Forge/Fabric loader and put the mods in their local %appdata%/.minecraft/mods folder.

Common Issues

Server Crashing? Usually caused by mismatched versions or missing dependencies (e.g., a mod needs a library mod to work). Check the Console for error logs.
Plugins not showing? Ensure you put them in the plugins folder, not the root directory.
"Mismatched Mod Channel List": This error means the player has different mods than the server.