When US currency was linked to gold, how was this done?
I think the only actual way to "back" a currency by gold would be to guarantee that a given amount of currency could be exchanged for gold. However, a few decades before Nixon, I doubt a citizen could take some dollar bills to Ft. Knox and exchange them for gold. So where did the exchanges of dollars for gold actually take place?
Most money in the economy isn't physical currency; it's just information about accounts. My understanding is that when a bank makes a loan, it effectively creates the money to make the loan. So if federal government indeed was trying to link dollars to gold, it had a complicated task. It had to regulate banks enough to keep the money supply from growing so large that there wasn't enough gold to back it.