It really depends on your server host, but in general our server host requires us to:
1. Use an FTP application such as FileZilla to upload the files to your server Mods folder.
And it is generally as easy as that. The server hosting company provides the connection ip and password to the FTP connection. It can be the same as your usual login information but the FTP port number will be different.
Other than that, it is exactly the same. Place the Mods in the Mods folder just the same as for Single Player.