Sometimes you can't find all plugins from the auto plugins installer, or if you developed your own plugin you want to test it directly into your server you can upload it via FTP.

Make sure that your server is using a version which accepts plugins. This can either be any version of Spigot or Bukkit, just be sure that the plugin is compatible with the server version. 

For this guide, I'll use the plugin Essentials from Spigot, because it doesn't anymore updated from Bukkit.

This version is compatible for all server up to 1.8 version. You can download it from Jenkins source.

In addition, you'll need the FTP client Filezilla or any other FTP client. 

STEPS: 

1. Download Essentials-2.x-SNAPSHOT.jar file and if you need other files.

2. Go to your control panel in the "FTP/MySQL" menu then open your FTP client and connect in using the credentials.

    After drag and drop the downloaded plugin jar file to the server's plugins folder. 

3. Once the plugin is into the server, restart it. 

4. Go the "Console" to read logs. 

5. As you can see the plugin starts correctly without any issue. 

Finally connect to your server to test the plugin. 

Check also our partner RyanGamerZ's tutorial.