How to rsync to an external HDD with TCP/IP ?

[SYNass IT Ubuntu / Linux]

Hello Ubuntu NW experts and cracks
Our 2 external HDD's work connected as TCP/IP or USB !!
USB experiments went quite well and now I am trying with TCP/IP !!!

One unit shall act as a Data Pool within the private NW by TCP/IP.
The second one shall act in Emergency cases connected directly with USB.

With the browser Ubuntu deals with this Data Pool unit:
It has a 200GB HDD and is FAT32 formatted and provides access with FTP
and Samba. 
Created are following folders: 

Backup
Private
Public

How do we rsync the backups to the existing Backup folder from my / our
notebook/s to this TCP/IP connected unit ?

I have absolutely no idea how to prepare this unit to get access !
Can you assist and guide me to get it solved ?

TIA for your appreciated hints and suggestions. ;-)
Cheers, svobi