This is about English speakers but I should think it works the same for the same sounds regardless of the language.
It's about where, in your mouth or throat, you make the sounds of the letters. M is with your lips, G is up on the back of your tongue. See?
I have had my tongue in there pretty far, but I have never touched the G spot with the back of my tongue.
I guess how it works for English is important because even though it's 3rd as the first language, it's #1 as a 2nd language, so still #1 globally. That's probably because of air traffic and business dealings.
I've not seen some of those representations of the sounds. Weird. Like the three-looking thing for the 'zh' sound (as in measure).
If I remember correctly (from my linguistic class in college), this wouldn't be true for other languages. Different languages have different phonemes (units of sound that make up all the words). There are some languages that don't use some of the ones we have and vice versa. That's why it can be hard to learn languages that don't have similar ones.
Here's a cool
site that has all of them