For Everyone who wants to travel to Iran, they have to use official guides, the ones who have a special certificate, they have a card that shows they have the certificate. This does not mean that you can not talk to people or ask them for directions or anything else or you can not make friends, but if you want to have someone to show you around you'd better get an official guide.

If you are an American, this means you need a special guide that has an extra certificate, a certificate necessary only to take Americans on tours.
Moreover, you can only travel within the framework of a tour, that is, you have to buy a tour, then you can travel to Iran.
I hope these complications are lifted soon after the nuclear agreement. But for now this is the rule.
Feel free to ask me more