How do you download content off of a DVD onto a flash drive?

It is actually not downloading. You just have to go your DVD drive, copy your desired content and paste it on the flash drive. Also ensure that there is enough space for your desired content on your flash drive.

It depends on the actual DVD format. If it is a write protected commercial movie, you will need a "ripper" app that removes the encoding as it downloads to a hard drive, or flash drive. That unencoded file can be copied between other storage devices from writing a new (unencoded) DVD, hard drive, flash drive, etc. Remember that it is illegal to make a ripped copy, but no one will say anything unless you use that copy for personal financial gain. IE: Pirating of a movie to make copies for sale to others, or to show that file to a paying audience is illegal. Mactheripper is widely used on Macs and I'm sure there is a similar app for Windows.

If it is a simple data, or game DVD you may be able to drag and drop to a flash drive, but if it has encoding to protect it, (many games do) you will need to "migrate" it as an .iso, which makes a duplicate that your computer sees just like it was the real DVD.

Use an authoring program.

copy/paste

FILE TO FILE COPY !

Rip the DVD to a media player library.

Copy the file of the DVD content to the flash drive.