People who can express themselves clearly and make themselves understood whenever you open your mouth: How the hell do you do that?

I stuttered a lot when I was younger. I usually think the sentence in my head before saying it.

I use somthing called my vocal cords…

“Speak low, speak slow, and don’t say much”
— John Wayne

Moreover: how can you not cry when you argue??

If you make a habit of typing clearly, eloquently, and with proper grammar it will influence the way you think. If you type like every letter is a Herculean effort, and your life depends on sending that text quickly, then that’s how you will express yourself generally as well. Review everything you write, edit it, and don’t hit send or post until it says exactly what you mean. I guarantee that will make speaking eloquently much easier, as you will become used to forming crisp, clear thoughts. You’ll also find yourself stopping and considering what you’re about to say before you say it. Also super helpful.