MISource uses a simulated application interface for the Let Me Try and Comprehensive exercises in the Access, PowerPoint, and Excel lessons. In the simulated interface, you can open menus without being judged immediately.
Sometimes, depending on how the question is worded, you can open a dialog box, and then click Cancel, without being judged incorrect. If the question asks you to open a specific dialog box, opening the wrong dialog box will result in "incorrect".
Remember, Let Me Try and Comprehensive exercises are scored as "complete" or "incomplete" only. So you can try each step as many times as necessary to get it right.