The electrical current in Spain is 220 volts, 50 cycles alternating current (AC); wall outlets take continental-type plugs, with two round prongs. An adapter from flat to round prongs is a must for computers and hair dryers.
Consider making a small investment in a universal adapter, which has several types of plugs in one lightweight, compact unit. Most laptops and mobile phone chargers are dual voltage (i.e., they operate equally well on 110 and 220 volts), so require only an adapter. These days the same is true of small appliances such as hair dryers. Always check labels and manufacturer instructions to be sure. Don’t use 110-volt outlets marked "for shavers only" for high-wattage appliances such as hair dryers.
Walkabout Travel Gear. This site has a good coverage of electricity under "adapters." www.walkabouttravelgear.com.