The money used in Chile is the "peso" (chilean peso, CPL). Usually the exchange agencies accept american dollars, euros, argentinian pesos, and brazilian reals. The exchange rates are approximately 1 CPL = 620 USD = 830 EUR. There are exchange agencies at the airport, which may take some extra comission for their services, but not much. There are also automatic cashiers that accept major credit cards and debit cards. In the airport one can pay the services in USD, but outside, only pesos or credit cards are accepted.
Health services are to be paid in Chile, either public or private institutions (no difference in practice). It is a good idea to bring a health insurance. One can buy an insurance at the airport on arrival, but it is better to have one at the departure country. The ICTP will provide an insurance to the foreign participants that do not have one, during the days of the school, but this will probably work on the basis of reimbursement. The organizers of the school cannot cost any health service.
To move in the public transport of Santiago in must buy a magnetic card (tarjeta BIP) at the subway stations, where it can also be recharged. For subway, one can also buy one way tickets, but these are no valid for buses. Buses can stop only at official stops (unlike two years ago).
Taxis can be taken at the street if the are free (LIBRE). There are also Radiotaxis, that are called by telephone. Taxi fares are rather low, usually they are 250 or 300 pesos for the first 200 m (for get into the car) and 100 pesos each 200 meters or minute.
Santiago is estimated to be a safe city, compared with other big cities of the continent (where I have never had a problem). However, it is not so safe as most European cities, and it is good to keep the usual cautions: (avoid darkness, do no bring attractive laptop bags, keep the cell phone well tighted). In case that someone claims your wallet or your cell phone, note that they do not act alone. You may run, but do not fight.