The ethernet network functionality is pretty simple. You have machines connected to a backbone party line. These machines broadcast their messages on this party line. If two machines broadcast at the same time, you have a collision where nothing meaningful is sent. In this case, the two machines wait a random amount of time before broadcasting again. Only one machine may communicate over the party line at any time.

A HUB changes the topology of the backbone from a line to a star shape. Machines still broadcast to every other machine on the network. Only one machine can talk at any one time.

A SWITCH is like a HUB except a SWITCH creates a dedicated communication line between two machines. More than one machine may talk at the same time if they are talking to different machines.

A ROUTER is a like a SWITCH except a ROUTER connects directly to a DSL connection (to the Internet) as well as to the local network. A router may also have other capabilities like provide a firewall and DHCP (Dynamic Host Configuration Protocol).