A lot of students struggle in the beginning figuring out how to fill a double stack magazine. While it takes some dexterity, its easy once you get a rhythm. Use 3 fingers to support the round to be filled on all sides. Support thumb presses down on top round in mag, firmly press the rounds down, under the feed lips, and use your thumb to slide it all the way back. That’s it! Practice and it becomes second nature.
Notice the word “fill” rather than “load”. Load guns, fill mags- important distinction from accidentally giving someone the wrong instructions at the wrong time.