Hi, txchain,
As Limos says, Handbrake is a good converter to use for your purposes. Mp4 is one of the most universally compatible formats, so I would go with that. Your USB drive should be formatted ExFat for use on a TV.
To begin, insert your DVD into the DVD player of your computer or an optical external drive. When the DVD's icon appears on the screen, click on it. You will see a screen that contains an AUDIO_TS folder and a VIDEO_TS folder.
Open the VIDEO_TS folder (ignore the AUDIO _TS folder -- you don't need it). Your home movie is contained in the files with the VOB extensions. (Ignore the other ones -- they are just data and back up files.) Option-drag (Copy, not move) the VOB files
out to your desktop, making sure that the originals remain in the VIDEO--TS folder. You can then open those desktop VOB files with the free download, Handbrake, and convert them to MPEG-4 videos that you can open and play, or import them into iMovie to edit and share out as movies.
You can get Handbrake here:
https://handbrake.fr/
A simple way to do it is to open Handbrake and do a File/Open Source. Navigate to your VOB video and choose it as the source from the resulting screen. Then do File/Start Encoding. Wait a couple of minutes for the conversion to complete. Then save and import the converted clip into iMovie.
-- Rich