essentially rather than generating a reply meant for a human, they generate a special reply that the software interprets as “call this tool”. in th same way as the system prompt where the model operator tells the system how to behave, you tell the model what tools and parameters are available to it (for example, load page is a common one)… when the software receives a call for the tool, it calls real code to perform an action, which then responds to the model with the result so that it can continue to process. in this way, the model may kind of request access to limited external resources