The international credit card such as (Master, visa … ) doesn’t work in Iran due to American sanction so to travel to Iran please bring cash with yourself.
The official currency is Iranian Rial ( IRR ) and official transaction is based on Rial but in daily life people use Tomans , you should delete one zero from Rial to reach Toman.
For example : if shop seller asks for 50.000 Tomans so you should add one zero and pay 500.000 Rials.
Some hotels , shops and taxis accept Euro or US dollar.
There is lots of official money exchange center in all cities and also in the airport which you can change your money to Iranian currency so easily.
Please notice that there is some black market for exchange in the street around exchange centers which is illegal so to find correct rate and receive correct note please make exchange in official centers.