i have seen people creating a forum(especially in graphics section) where if you thank the forum, then only some content will be visible, otherwise it is hidden. how do you create such forum?

I think it is default for the "Graphics Tutorials and Resources".
You have to thank the post in order for you to view the Tutorial.

so, you can't make such forum anywhere else? and to make such forum in tutorials, all we have to do to make it like that is to make it like we normally do?