iDVD & 3 movies

[Joan Keenan]

I'm ready to use iDVD for the first time, but want to include 3 movies, 
one of which I want to break into 6 chapters I have that one ready to 
burn, but how do I add the other movies. If I open them & go to export 
to dvd they open a new idvd screen. I tried going to export to dvd, but 
that says it is not necessary anymore & opens iDVD at a new screen!
How can I get all the movies on one dvd....they are not long. I'm sure 
there is an easy way...but I can't find it.
Thanks in advance for your expertise.

Joan