Unfortunately, sometimes advice can seem contradictory. Until recently I've always been under the thought that the speculative reader would hold questions in abeyance and/or would read into the implications.

In his book, How To Write SF&F (Chapter 4), about Exposition, OSC gives an example regarding Octavia Bulter's Wild Seed. There the viewpoint character thinks about his
'seed village'. The viewpoint character would not stop and think about what a seed village is, he wouldn't give it a second thought. The reader has to watch the story unfold to figure it out.

But the reader will likely anticipate what those words mean. If the character stopped and explained, they would lose all credibility and perhaps there voice.

I've thought this was in conjunction with the R.U.E. principle, wherein one has faith in the reader to put the pieces together.

In a short story, a good hook might be to put the protagonist's name (character), where the protagonist is (setting), and a hint about the situation or problem facing the protagonist in the first sentence.

(Now, everyone go look at a bunch of published short stories to see how many writers actually do that. This is known as "the writer's reality check" and should be applied to every piece of writing advice you ever receive.)

If you can get a character, a setting, and a hint of the situation or problem (or goal the protagonist is going to work toward in the story) into the first 13 lines (if not the first sentence), then you have a good chance of achieving a "hook."

Of course, it can take longer than 13 lines in a novel, but if you remember that many readers decide whether to buy a book or not by opening the book and reading the first sentence or so, you may understand why it is that the earlier you can hook a reader, the better.

When someone posts their first 13 lines, and the people ask about point of view or about the situation or about where this is happening, they are asking for the three things I listed above: a clearly identified and identifiable character (POV), a place they can visualize (setting), and what's going on there (situation). They are trying to help you hook your readers.

Writers write, and what we write, in most cases, can be looked at as explanations of one kind or another. So it's very hard for writers to RUE (resist the urge to explain).

The trick is to figure out how much to explain, or how little. And that's why the Fragments and Feedback area can be helpful.

Try putting as little as you can into those first 13 lines, but at least put in the point of view of a character, the setting, and a hint of the situation.

Those who read your first 13 lines will tell you if you need to put more, and what that "more" may need to be to help them to care about ("so what?"), to believe ("oh, yeah?"), and to understand ("huh?") what you are writing.

The other RUE (readers understand eventually--I thought that's what it was, too, by the way) you will have to take care of AFTER you get them to read beyond your first 13 lines.

We want to find out more about the character because of what we've already learned about him on that first page. But consider if Butler had invented an unexplained and not particularly meaningful phrase to use instead, like "Buthondlia". Then we wouldn't know half as much, and we'd know that we were being cheated out of POV information, because the POV knows what "Buthondlia" and is currently thinking about the subject.

There's an important principle behind the reader's willingness to keep reading so as to figure it out eventually. The reader should have faith that the writer will reveal everything. And that faith has to be based on what the writer has done so far. If I get the feeling, after reading the first couple of pages, that the author is screwing around and withholding information known to the POV, then I won't have much faith. If the writer is always giving me the information that I want most as soon as possible, even when I didn't know that was the information I wanted until the writer gave it to me, then my faith increases.