Don't be fooled, like I was and expect any video/audio editing capabilities from iDVD. It's simply a bare bones GUI used to create titles, backgrounds and menus for previously created video
with audio in them.
However you create the video and audio, they should first be combined/edited in iMovie. You can also add 'markers' ( with text titles ) that can/will then be used by iDVD to create 'chapter' divisions and scene titles. The menu 'things' in iDVD, should you choose to use them are simply the bits of video you created in iMovie.
These programs are less than intuitive for those of us who have never worked in video, from my experience. Terms such as 'chapters', 'scenes', 'markers' may mean different things to the un-trained than what they mean in these two programs. If you have dotMac, I recommend viewing the tutorials there on both programs and visiting some of the forums that discuss these apps. Then, play around with them for a while, creating small movies/DVDs and generally learn what happens with what! It ain't rocket science, but it
is different! At least it was for me.