The global market is avaialble in the survival worlds to all the players.
You can buy and sell items here.
To browse what's available, type /market
To buy an item, hover over it, read things carefully, and click it.
Then click the green confirmation.
To sell an item, hold it in your hand, and type: /market sell amount, for example, hold a dirt block and type: /market sell 15
This will then put the dirt block up for sale on the global market for others to buy, if they do, you will get your money.