Tool calling lets an AI ask the application to use an approved tool, such as a calculator, a search function, or a way to look up an order. The app runs the tool and gives the result back to the AI.
Think of the AI asking a helper to check a number before finishing an answer. The AI chooses when a tool may be useful, but the application controls which tools exist and what they are allowed to do.
A request to use a tool is not the same as proof that the action succeeded. The app should check the result, and sensitive actions may need a person to approve them.