With the takeover of the Eugenists, hard cash went the way of the dinosaur. To do any business transactions in Night City, you're going to need a credstick from a bank. Once you've got a credstick, you can look at it to see how much money you've got in your account. You can transfer money to other players or shopkeepers with the "pay" command:
pay <who> Pays a shopkeeper whatever you owe em. pay <amount> to <who> Pay a person a specific amount.
Making money isn't easy for those of us in the underground. Salvage is a good start; many found items are sellable in the various stores. And while it's dangerous, murder and robbery are not too cruel for many of us. For the more noble, the WasteLands offer an opportunity: certain organizations will pay handsomely for ancient artifacts.