The Chilean unit of currency is the peso (CH$). Bank notes come in denominations of 500, 1000, 2000, 5000, 10,000 and 20,000 pesos. Coin values are one, five, 10, 50, 100 and 500 pesos, although one-peso coins are fast disappearing, and even fives and tens are uncommon. Carry small bills with you. It can be difficult to change large bills in rural areas, try gas stations and liquor stores by asking, '¿Tiene suelto?'.
Exchange rates are usually best in Santiago. Chile's currency has been pretty stable in recent years. The value of the dollar seems to decline during peak tourist season and shoot back up again come March. Paying a bill with US cash is sometimes acceptable, especially at tour agencies (check their exchange rate carefully). Many top-end hotels publish rates in US dollars with a lower exchange rate than the daily one. It's best to pay all transactions in pesos.
Money wire-transferred should arrive in a few days; Chilean banks can give you money in US dollars on request. Western Union offices can be found throughout Chile, usually adjacent to the post office.
It's customary to tip 10% of the bill in restaurants (the bill may include it under 'servicio'). Taxi drivers do not require tips, although you may round off the fare.