First of all, welcome to Puzzling.SE, and thank you for checking out our help center!
I recognize that this is a hole still in our Help Center documentation, and I actually have it on my list for today to start a new Meta discussion to this effect.
In short, what you need to know to get started are the following things:
- The standard Stack Exchange on-topic qualifiers still apply. This means that if your question is too broad, unclear, primarily opinion-based, or some such, it's not on-topic here, just like everywhere else on Stack Exchange.
If your question is about the creation or solving of puzzles, it's primarily on topic. If your question is a puzzle, then generally speaking it is on-topic too.
There is one category of puzzles that we have identified we are not quite as fond of: puzzles that fall under a midpoint between too broad, primarily opinion-based, and unclear. We've created a custom close reason for this.
The primary reason I think we haven't really felt pressured to fill in this section of our help center is pretty simple: we really don't have too many limits on scope at this point beyond "does it relate to puzzles?" If your question does, it's probably on-topic (with exception above).
It's also worth noting as an addendum that questions aren't closed necessarily - they're just put on hold until they can be improved or reworded. Without knowing the question you're trying to ask, there's no way to know if the criterion above will apply, however, and some questions may not be feasible to reword.