How do I filter the posts by multiple categories? For example, if some of my posts are categorized under just apples and some as just oranges and some both, how would I filter the results to show only posts marked under both apples and oranges?

In other words, I don’t want the results to list all posts under apples and all posts under oranges. I only want to show posts listed under both apples and oranges. Is there a way to do this?