Definitely never let a beginner practice on your own car if it can be avoided, each grind will make you wince.
That being said, I learned the basics of driving a manual transmission (mainly just shifting and when to do so) by playing Gran Turismo 3 lol, driving that ugly Sprinter Trueno. By the time I jumped in an actual MT car, the only thing I didn't know was that the clutch had to be pressed to turn the car on, took me 10 minutes to figure that one out :sneaky:
I definitely wasn't an expert, but I was better off because I had the concept nailed down pretty hard. A day of occasional gear grinding and sudden stops from letting the clutch go in an actual car was all it took.