In essence, a hub is a repeater: when it receives a bit from an adapter, it sends the bit to all the other adapters.
In this manner, each adapter can (1) sense the channel to determine if it is idle, and (2) detect a collision while it is transmitting.
But hubs are popular because they also provide network management features.
For example, if an adapter malfunctions and continually sends Ethernet frames (a socalled jabbering adapter), then a 10Base2 Ethernet will become totally dysfunctional; none of the nodes will be able to communicate.
But a 10BaseT network will continue to function, because the hub will detect the problem and internally disconnect the malfunctioning adapter.
With this feature, the network administrator doesn't have to get out of bed and drive back to work in order to correct the problem.
Also, most hubs can gather information and report the information to a host that connects directly to the hub.
This monitoring host provides a graphical interface that displays statistics and graphs, such as bandwidth usage, collision rates, average frame sizes,etc.
Network administrators can use this information not only to debug and correct problems, but also to plan how the LAN should evolve in the future.