Like most of continental Europe, Spain outlets have a voltage of 220-240 Volts and require plugs with two round pins. Many appliances such as laptops, camera chargers, and mp3 players have chargers with built-in converters that can handle European voltage (look for this information on the charger itself). Check to see if there’s a switch you need to flip somewhere on the charger or if it converts the voltage automatically. When there is a built-in converter, all you need is a plug adapter which can be easily purchased before leaving the States. If, however, you have chargers that can’t accept this voltage, you will need both a plug adapter and a voltage converter (often this can be purchased as one combined item).
Sometimes it makes sense to get a travel adapter kit since there are several countries nearby (such as in the United Kingdom) that require different plugs from those used in Spain.
Appliances that use a lot of heat such as hair dryers, straightening irons, etc. often burn out when used abroad even with converters, so we recommend you leave those home (you can always buy them here if your homestay doesn’t have what you need). For more information on this topic, here is an informative article from CNN.