A run that hits something it cannot responsibly decide stops and asks, rather than inventing an answer and carrying on.
When it asks
Typically when a value it needs is not in your model or its sources — a conversion rate, a contract term, a decision only you can make.
Where the question appears
On the task itself, and as a notification if you have those on. The run holds its place while it waits.
Answering
Type the answer. The run resumes from where it paused, and the answer is written into the work — cells update, downstream figures recalculate. You do not re-run anything.
Not answering
A question left unanswered becomes an issue you can come back to. The run proceeds with a clearly-labelled placeholder rather than stalling forever, and the placeholder is visible in the result so you know a number is provisional.
Stopping and restarting
You do not pause a task by hand — it pauses itself when it needs you. What you can do is cancel a run, and restart one. A restart does not begin from nothing: the run keeps checkpoints as it goes, so it resumes from the last one rather than redoing work already done.