When traveling to Europe you'll probably want to bring along an electronic device or two. Occasionally outlets can be inconvenient to reach and an extension cord may help. If you have room in your bag, a cord from home may come in handy.
American plugs use a double slot and tab system and our electricity runs on 110V. In Europe, the plugs are two holes and two prongs with a voltage of 220V. A converter converts the higher European voltage to the lower American voltage. An adapter has one side that fits into the European outlet and one side that accepts American plugs.
Check to see if you need the converter before using it. If your device (usually on the charger for gadgets) says "110-240V," no converter is needed and you can plug it into the adapter to charge. For items that don't have this range (usually hair dryers or other beauty appliances) you will need to plug the cord into the converter, the converter into the adapter and the adapter into the wall.
The use of an extension cord from home will allow you to make use of hard to reach or inconveniently located outlets. In this case you will plug your device into the cord, the cord into the converter (if needed), the converter into the adapter and the adapter into the wall.
If you have an extension cord with multiple outlets, check to be certain the electrical system can handle the load. Also, if you don't have your own extension cord and borrow a European one you will plug your device into the converter (if needed), the converter into the adapter, the adapter into the European cord and the cord into the wall.