The local currency, the Macedonian denar, is fixed at about 62 denar to the euro, which makes it about 40 denar to the dollar at a dollar-euro exchange rate of 1-to-1.5.  Major items (hotel rooms, long taxi rides, BMWs) are often priced in euros, and you can pay in euros or denar.  Normal purchases are priced in denar, and you should pay in denar.  The only thing you can do with dollars is exchange them for denar; there are plenty of money changers.  But the easiest way to get denars is to use a debit card in an ATM; they are all over.  Be sure to tell your debit card company where you will be using the card.  Bring some cash to fall back on while sorting things out if there is a problem.

You should make sure that you a) keep the receipt issued by the ATM when withdrawing money and b) try to use an ATM that is operated by a bank with many branches across the country, e.g. ProCredit rather than a local bank. 

denar

The reason is that you cannot change MKD (Macedonian denars) outside of Macedonia so you will need to change any money back to Euro, GDP or USD etc. before leaving Macedonia.  If you wish to change money in the bank, you will need to produce the receipt from your original withdrawal and you will need to go to a branch of the same bank that you withdrew the money through.  Otherwise, you will not be able to change your money through a bank and will have to go through a private exchange office or Western Union or the like.