The basics are easy - half an hour with someone who knows what they"re doing should be all you need to get out and about. Getting to the point where it’s instinctual and you don’t have to think about shifting is probably beyond the limits of a short trip but depending on how much driving you do you can be fairly smooth within a few days.
The main risk you run with learning manual is that once you get the hang of it it spoils automatics for you - you might end up having to buy yourself a manual car to avoid being annoyed by the missteps autos tend to do.
Descent was one of the first games I had to play, I remember it fondly. It came bundled with my family’s first computer (along with Lemmings and Simcity 2000) so I spent a fair amount of time on it. The freedom of motion you had in Descent was impressive - albeit easy to confuse yourself with - and something I have rarely seen since.