Weak public speaking isn't because people don't know "how" to do it. It's a vicious cycle made up of self-defeating beliefs and behaviours:

You believe you’re bad at public speaking >> you feel self-conscious >> you try to make yourself invisible by rushing, mumbling, and apologizing >> you catch yourself rushing, mumbling and apologizing >> you conclude that you’re bad at public speaking.

Luckily, there’s a way out of Public Speaking Purgatory.

Maybe you're right. Maybe public speaking isn't for you. Maybe you should avoid it completely, never share your ideas, never take the risk, and never find out what might happen if you tried. Or maybe it's time to take a closer look at the story you're telling yourself.