I am completely confused with meta. When I post a question people scream that it is duplicate and downvote. And they recommend me to comment the original post. If I do they downvote and scream it is off-topic. Whatever I post on meta is wrong. Is there any allowed way how to participate in meta? It seems to me that the most subjects were already covered and if it is not allowed to discuss existing topics, then it seems to me that meta is locked for participation. :-(
The most important thing to understand about Meta is "There is no they." There are a number of people who may disagree with each other. If you bounce around like a pinball trying to avoid angry people screaming at you (which, by the way, is a mischaracterization of the comments on your answer) you will never be happy.
If you have a question, start by searching. If someone already asked, great! You have your answer. If you can't find it, ask. Perhaps it will be marked as a duplicate. This is still great! This is not someone screaming at you. You have your answer. And the site has another way for new people to find that answer, when they search using your words.
Never ever post a question as an answer to another question, or as a comment. That's not how meta works. If you do, your "answer" will probably be deleted, and people will tell you that you did it wrong. The system is self correcting.
Why do you want to "discuss existing topics" anyway? Do you want to learn more about a feature? Then don't ask vague and general questions, ask highly specific ones and include links to the related questions you've already read. Do you want a policy or practice to be changed? It's rarely a good idea for such a question to be your first - it requires a fair amount of background information to make a good feature request.
And most important, do not read emotion that isn't there. Downvotes, calm comments that "this doesn't belong in this section", and close votes are not screaming. Don't take them that way. (Trust me, meta does scream from time to time but those posts tend to get deleted so you won't have seen them.)