If you are foreigner in different country, exchanging money can be really costly or you could just take advantage of it and even make some money. In most of the countries the banks offer foreign currency account and they will link that account with your local account. For example if you live in Europe and you have euro account then you can also open US dollar account or other currencies. When you send money from your euro account to USD account or vice versa, you will save money on because banks offer best rate when you make transactions among your accounts.
If you live in US or in Europe and you don’t really know how the forex trading works and if you want to hold your foreign currency for longer because you predict it will change in longer period of time then you can use your currency accounts and do exchanges among your accounts.
Since I have strong finance and economics background, I love predicting the currencies. I know the types of information that will give small abnormality on the exchange rate.
Another advice I can also give is that when you make international transactions use the currency accounts rather than your local account. For example if you study in US and your parents from Europe wants to send money to your account then let your parents send money to your euro account in US. Alternatively, your parents should send money from their euro account to their own USD account in Europe and then send from their USD account to your USD account in US.
It is almost impossible to make so much money on exchange rate with small money because the margin is very little, but you can save a lot of money if you are going on holiday or if you need to exchange a lot money.