Some ancient history
In the old days, we used to slim-jim cars to open ‘em. (Actually, other people did. I stank at it and still do.) If you watch the movies, it’s as easy as hotwiring and takes just moments! In reality, it takes some time (though some folks are lightning fast). Those folks are usually wrecker operators, not thieves.
The idea was to get between the window and outer door skin and operate the door latch or lock rods to gain entry. Vehicle manufacturers began implementing measures like bends and baffles in doors to prevent this, and at the same time, they also began moving away from mechanically operated latches and locks, though you’ll still find plenty of those in service.
Nowadays, though, the modern lockout kit focuses on gaining entry between the vehicle door and body, because that works on most new vehicles and a pretty good portion of the old stuff.
Practice with a slim jim if you like, but only after you’re proficient on the modern tools—they’re a lot easier. Let’s start learning about those.