Iran currency is Rial. But during your trip to Iran you will hear that people or shop keepers say Toman instead of Rial. This is what some travelers mostly have problem with.
Toman is one tenth of Rial. For example a shoe cost 560.000 Rial but the shop keeper tells you 56.000 Toman or 56 Toman. As you see for Toman you omit one zero from Rial and it changes to Toman.
Rial mostly use for official works like banks but the best way is to ask them the price is Toman or Rial.
The tourists who travel to Iran cannot use their master card or visa card because of sanction on banks of Iran. So travelers need to bring cash for the entire of their stay on Iran. You can bring Euro, US Dollor, UK pounds and you can exchange them in banks or Sarafi. Sarafi offices offers you better rates. You can find Sarafi offices mostly close to your hotel, touristic areas, airport, hotel receptions, and large cities.