Search Modrinth from your server panel, install, restart. Here is how, and how to avoid plugins that won't load.
Install a plugin from Modrinth
Open Plugins in your server panel.
Search Modrinth for the plugin you want.
Pick a version that matches your server software and Minecraft version.
Install it, then restart your server so it loads.
Plugins or mods?
Plugins run on plugin software such as Paper or Purpur. Mods run on Fabric. If your server uses Fabric, use Mods instead of Plugins in the panel.
Upload a plugin that isn't on Modrinth
Download the plugin's .jar file from its official page.
Open the file manager in your server panel.
Upload the .jar into the plugins folder.
Restart your server.
If a plugin doesn't load
Most problems come from a version mismatch. Check that the plugin supports your server software and your exact Minecraft version, then restart. Take a backup before adding several plugins at once, so you can roll back.
Common questions
Do I have to restart after installing?
Yes. Plugins load when the server starts, so restart after installing or removing one.
Can I use plugins on the free plan?
Yes. The plugin installer is included with every plan.