Subpictures setting dvd fab 5

Hi, I just joined the forum. It seems to have a wealth of info and very helpful people, thanks. I am NEW to dvd fab and I,m sure I will have alot of questions for the experts here.
One question I have is in dvd fab 5, what is meant by subpicture ? Is this subtittle? and how do I set it to make sure it picks up subtittles in movies? thank you.