Can I copy video clips from a DVD ...
Bill74maybe wrote: ... to use in the Imove Library and use them to compile a Project...
Not if you mean from a DVD video. While you can copy the files on a DVD video to other Mac disks, they are not in a format directly useable by iMovie. Moreover, if they are commercial DVD video disk files, they are likely copyrighted so as to prevent their use in your iMovie Projects anyway.
Bill74maybe wrote: ... or do I have to use my Sony camera to download clips from tape exclusively? ...Bill
No, not exclusively. Use your Mac's iMovie > Help menu command to search for "import" (without the quotation marks. You can also look in Apple Support for articles like iMovie '11: Import video from movie files or other articles from a search like this one. You may also be helped by some of the tutorials and other info in iMovie Support.