Probably the best place to start is Edward Troxel's excellent Vegas newsletters.
This issue is one that discusses authoring a DVD. There may be others; search the index.
Markers are points in time on the Vegas timeline. You can export them when you render video and DVDA will pick them up so you can use them as chapter points.
Regions are, well, regions on the Vegas timeline. I don't believe they have anything to do with DVDA or DVDs.
Check the online Help file for more details about how markers and regions work.
Good luck.
Dennis