The Sharjah port is called Port Khalid and is located at 25°21.457’N 55°22.614’E.
To get there from Dubai with public transport, get a bus from Al Ghubaiba bus station, Dubai, to Sharjah, ask to get off at nearest stop to Khalid Port. Taxis will take you to port for 10-15 dirhams.
The passenger terminal is behind the customs office. For passengers without a vehicle, check in there and get a boarding card, and check in any luggage you don’t want to take on board. Wait in the passenger waiting room until you get sent through to immigration in adjoining room to be stamped out of UAE, and then bussed to the ferry.
There is ATM inside the immigration building in Port Khalid. There is no money exchange inside or outside the port, though. Changing Iranian rials can be a challenge in Sharjah. Get rid of it before getting on the boat in Iran, or try Salim exchange.
If you are looking to take a ferry from UAE to Iran, see following articles: