there is good example of bitcoin and real money we can use bitcoin for online shopping for online website who sell their product for online and real money we can be use for local shopping in local shops and real money have physical shape.
yes actually the number of bitcoin users are very low, so we can expect in future when the number of bitcoin users will increase then bitcoin will certainly give us some useful facilities, and we will be able to use bitcoin as fiat in local market for buying and selling good and for so many other activities.
To me the main difference is future and past. Bitcoin is the future and the real dollar etc is past. As world is going to be digitized so there would also be need of digital currency which is bitcoin. So this is the start and in future our names will write in history that we were the very early users of this currency.