I bought the mac because I thought it would easy to do this type of thing.
Until about a year ago it was.
Purchase iLife 11 (includes iDVD) on disk.
IDVD is a wonderful piece of software and well worth the low cost of $40.
Yes, there are programs that will put a movie on a DVD. I have tried most of the other substitutes including Toast, Burn, Wondershare, and others. None of them come anywhere near the ease-of-use and power of iDVD.