The euro is the currency for most of Europe, twelve countries in total, including France, Germany, Spain and Greece. If you are travelling in the 'euro zone' or coming stateside from one of the Euro 12 you will convert euros to dollars or vice versa. The dollar and the euro are both divided into 100 cents, so this makes mental conversion a bit easier to wrap your mind around. However, a euro and a dollar are not equal. The value of each fluctuates according to the market of the day.
The best place to exchange your currency is through your ATMs. The conversion fees tend to hover around 1%. Not all places charge the same fees and hotels can be especially pricey, upwards of 10%. ATMs are omnipresent, simple to use and will give you the best up-to-date rate.
You know where to exchange currency, and how to get the best rates, last is understanding who has the strongest currency, your dollars or the euros so that you know exactly how much you want to convert and what will give you the most bang for your buck. Many cafes and hotels have internet access and you go online and get the live rates from sites such as XE http://www.xe.com/ucc/. A quick formula for conversions:
USD x [foreign exchange rate] = foreign currency
[foreign currency] / [exchange rate] = USD
Bon Voyage!
