Why do I always have "not bold" Thread title when i start a new thread,but many people has bold thread title when they start a new thread,tell me how did this happen pls,i wanna get a bold thread title,i realize most of the Art/Items thread starters with bold thread titles is more "popular".I wanna fix that,tell me how to,pls.

The bold title just means that there's content which you haven't yet seen. Since you write the contents of a new thread which you make, you must have read it so it isn't bold. It is bold for everyone else, though.