MyBB Community Forums

Hi fellows,
I need little help that I want that the guest will see the forum and also sub forum also can see the post but when guest want to open that post, he/she will see a message to register to view the post. I hope you guys will guide me that how can i do this?

I wouldn't do this. If people can't see your content, it is going to drive them away. I know I have left a few forums because of this type of thing.