These are all the mods you have downloaded. You will see a bunch of folders with numbers.Open the folder names 211820 (Starbound Steam ID).
Non-workshop mods are installed the exact same way on the server as on your computer simply use the File Manager on the left side of your panel to access the server's mods folder and upload the mod files. There are two ways to get workshop mods for your server. How Do I Install Mods On My Starbound Server?