I have some ideas for future moviemaking. Can I discuss about them here?
No, not on this site.
This site, Science Fiction & Fantasy, is for questions and answers about existing works of science fiction or fantasy, either specific books/films/etc. or questions about the genre as a whole.
Maybe somewhere else, depending on the question.
Your query is very vague, so it's hard to know exactly what you intend to ask. If it's a question about the creation of fantasy worlds, then Worldbuilding SE might be a good bet as other answerers have suggested. If it's a question about the process of movie production, then you might try Movies & TV SE (possibly - I'm not sure whether such questions are on-topic there, or if they like us apply a policy of "questions about existing works only") or Video Production SE (whose scope I don't know at all).
Before asking on any site, though, you should check their help centre to see if your question is likely to be acceptable there or not. Every site has its own help centre page to explain which types of questions are on-topic and which are not.
No, questions on this site should generally be about existing works of science fiction or fantasy. Depending on the question you could try Worldbuilding. However, I think it would need to be a specific question relating to building the world. Asking in general as in: would this film idea work? Wouldn’t be acceptable there or any SE site as far as I know.
There is a whole Stack devoted to questions like the ones you want to ask called worldbuilding:
Worldbuilding Stack Exchange is a question and answer site for writers, artists and others using science, geography and culture to construct imaginary worlds and settings. It's built and run by you as part of the Stack Exchange network of Q&A sites. With your help, we're working together to build a library of detailed answers to every question about worldbuilding.
Head on over and knock yourself out!