Requirement: Your server must be running a version that allows plugins (Spigot, CraftBukkit, Paper, Purpur, etc.)
Login to the panel (https://panel.nexussociety.net/) and click on your server. Click on files and go to the plugins folder. Then just drag and drop your plugins that you have downloaded into this folder and restart your server!
You can also connect to the SFTP of your server, click on the plugins folder and drag the plugins you have downloaded into that folder. Restart your server through the panel after doing this!
Remember: Make sure the plugins you are uploading are compatible with your server's server.jar version, the one included with Nexus Hosting without any modification is the latest version of Purpur Spigot
Video made by one of our managers on how to add plugins (You can set it to 1080p in the video settings!)