A shared format for information
JSON can describe a customer as {"name": "Ava", "orders": [42, 57]}. The labels name and orders identify a name and a list of order numbers. A shop’s API may send this text to another app so it can show the customer’s orders.
A format, not a guarantee
JSON tells software how the information is arranged, but it does not prove the details are correct. An app still needs to check that expected details are present and values make sense. JSON can be saved in a file or sent between systems; it is not itself a database.