The best thing is to put the DVD in and insert a flash drive and then see what messages/instructions come up.
Put the DVD into your computer and let it load.
I get the option to Import, or you may be able to right click and get various Copy options
Then you can save to hard drive.
Then put in flash drive and copy from one to the other.
You may be able to miss out a stage and import it straight to the pen drive.
Actually likely to be far from simple. Almost certainly not a simple copy and save instruction if the DVD is a commercially produced film. You could try using one of the freely available programmes for this purpose but don't expect an easy ride!