Edit: Why is this question marked as dubplicate? In this question I asked to search for questions without a specific tag. The question mentioned is "How do I search for questions with specific tags?" ?
Use negation. In other words:
(You must also give either a search term or operator. In your case you want only questions, so
From search help:
To exclude results from a tag, term or phrase, prefix it with
-in your query:
waffles -unicornsfinds posts that mention tasty batter-based breakfasts without including mythical creatures, while
[laurel] -[hardy]includes only posts pertaining to the first half of the classic comedy couple.