A hub is a common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. It contains multiple ports.
When a packet (of data) arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.
If you are referring to the BT Home Hub, it also has the capability to interact with a fusion phone, give VOIP and BT vision and is a router. It interfaces with wired and wireless connections to computers. You can only use two wired computers unless you use a supplementary hub