That has nothing to do with what he asked.A USB hub is a small, light unit with multiple ports for plugging in USB devices. It is commonly connected to a USB port located on the back of a desktop computer by using an extension cable. A USB hub is also great for laptops with only one or two ports. Most hubs can support up to 127 devices.
Again with the posts that have nothing to do with the original question...It depends on what you have plugged into the hub, the hub should have come with a information leaflet, the more powerful items you have conected the more power its going to need so then you need to plug the external power source in, if its just for..an MP3 Player you can let it run of the computers power source.