The device may explode or experience a meltdown. The switch will begin to vibrate violently and may explode, too. Please NEVER plug a device into a switch without wearing goggles and an anti-blast suit. :-)

All kidding aside, in the most common application, switches are used to allow computers, IP phones, laptops, and any other networked device to access a network. That switch is usually connected to more switches or a router, etc.

Tons can be written about this. You shoud real some books.