We have no requirement on what you do with the worlds you build. It's sufficient for you to just imagine the world in your head. We do however expect that you're actually building a fictional world.
If you frame it right, most questions can be about worldbuilding. For a question to be appropriate here you must make sure that as written is about worldbuilding. As long as your question shows clear worldbuilding purpose it will be considered on topic for this site. You may still want to avoid asking questions that can be answered with a simple Google search, or that are entirely about real world physics, chemistry, etc.
Please don't ask pointless questions. The SE model is all about creating a repository of high quality answers. Good answers tend to come from good questions, and the best questions are those that are motivated by some specific need. This allows the answerers to provide additional explanation and relevant context, which is part of what distinguishes a satisfactory answer from the truly great.
In short as long as you come to us with a good question about a real worldbuilding problem you're having you shouldn't have any problems on this site.