Final answer:
The Forward button on the Internet Explorer toolbar becomes active after the Back button is used, enabling users to navigate forward to the page they came from.
Step-by-step explanation:
The button on the Internet Explorer toolbar that only appears active after the Back button has been used is the Forward button. When you navigate back to a previous page using the Back button, the Forward button becomes enabled, allowing you to return to the page you were just on if you wish to do so. This is part of standard web browser functionality where the history of pages you've visited is maintained, allowing for easy navigation back and forth between recently visited pages.