Money represents work. When you do work, you get money. When you want work done, you give money to someone else. That's fundamentally what our economy runs on. You could argue that some people take advantage of this on the top, but the vast majority of any economy is based on people doing work. The dollar is backed by the US government. When you go to a store and say you want to buy something, they have to take your money. In fact it's illegal for someone to not accept legal tender. That is the value of the dollar.
So now you say, but the US government isn't anyone special. Countries come and go in dominance, why is the dollar worth more than any other currency? Because their really is no other country with which everyone else wants to trade with on a massive scale. Americans are willing to give more money for work than any other country, so it is in other countries best interest to take dollars, which in turn increases the demand for said dollar.
Wouldn't it be useful for a digital currency like bitcoin to replace all of that? Not really, unless it has actual ties with actual money. A digital currency's only real value is being able to send and receive money, fast. But once it gets wherever, it still has to be converted back to the local currency. Gold and other commodities have physical values with physical properties than can physically do things. That in itself makes them have a base value, when they go up or down, that's just the market being the market.
You could start talking about how more companies (like Microsoft) are accepting bitcoin, so potentially you'll never have to convert it back to local currency but that conversation leads to the dollar being essentially worthless and the US government could collapse any minute and you should save all your money in bitcoin. Which sounds stupid and goes into pump-and-dump territory.