How to Admin or the person who create the topic can only post

[joffreyjaffeux]

Generally speaking please have a look at howto - Discourse Meta

I think you should be able to fix your issue with:

How to create private categories using category security settings

This video explains how you can use group permissions to create private categories (or private “forums”). Scroll down for written instructions. [How to create a group and add permissions to a category] The Security tab on the category edit page is used to control both the visibility of categories and what users can do in a category. This is done by defining an access list of groups that associate a group name with an access level. The default permission for a new category is that t…