The difference between a switched network and one that uses hubs is a concept that confuses many people and will be explained here. The short answer is that a switch has intelligence and communicates with every device connected to it. This results in a significant performance increase, although at a much higher price. A hub is not an intelligent device. Basically, it connects all of the devices to a single pipe and lets them determine on their own how to move data between them.
Data is moved in packets, with each packet having a source device and an end device.
If two devices want to move data at the same time, the one that requests it first gets it first. The second device has to wait until the pipe is available. A and then another to device B, so that they share the pipe equally. Or, there may be a priority system set up depending upon what information is being requested. A video file, for example, may somehow have priority over a data file, resulting in a long wait for the device requesting data versus a device requesting video.