making post under pages for users

hi, i got problem with Wp and i don’t know how to create that users could make posts under my pages.
For example on my website: http://www.your-idea.eu/
that i have page travel idea’s, i want to make that user that would come under these section that he can make a post under that page. And that the others may comment that post that some one made. I hope you understand what i mean. So if there is any plug-in i would be realy happy of it, or any template. By the way im new to these 🙂