The voltage used in continental Europe is 220 Volts. This renders most American appliances useless unless they are convertible, battery-operated or you have an adapter. In the US, adapters can be bought at every major electricity shop. Note that the outlet geometry is also different. Outlet adapters also exists that switch between the different systems and are available in the US for a few dollars.
Today most general use electronic devices (such as laptops, portable CD players etc.) come equipped with a built-in conversion system between 110/220 Volts (but not between the mechanical outlet geometries). In such a case all you need is the mechanical adapter. In case of doubt students should check their devices and consult the Program staff in advance.