In addition to extending the Ethernet port, as opposed to giving you an extra one, this port replicator includes four USB ports, a VGA video output connection, and a power supply connection. The main use for this kind of replicator is that you set it up on your desk with all your connections plugged into the replicator instead of the PC. That way, when you get ready to take the PC with you, the only thing you have to unplug is the port replicator.
Most port replicators also include PS2 connections for a mouse or keyboard, but this one does not. You could always get a USB mouse or keyboard to use, but that would take up 2 of the 4 USB connections it gives you. At least it does include a VGA connector for hooking up an external monitor, which is always good to have when people don’t like the smaller laptop screens.