It isn’t quite clear to me exactly what you are asking when you say “meta description displaying in the main category”. Technically, the meta description does not display in the browser. So, I assume you are talking about the category description. Please clarify this point and I will try to help.
Generally speaking, you want to have a unique meta description for each page. The meta description is embedded in the code and does not display in the browser.
The “Manage Categories” section in the Magento admin panel will allow you define the Category page Description, which displays on the page, separately from the Meta description, which is embedded in the page and not displayed in the browser.
Please clarify where you are having difficulty and I will try to help.