Locked posts info

Hi Stephano,
I know I’m not terribly computer savvy, but I just don’t understand how to lock a section. I have some ebooks I want to put under the catagorie “Reserved” and I have made a main menu tab for this. When I add the post, I put reserved in the tag and put [newsletter_lock] then the ebook then [/newsletter_lock]
But how do I tell if it has worked and then how do I let people access it?