Ask HN: How to learn to document and demo a software product?

I'm a developer and every time I want to demo my projects, I struggle to draw diagrams (functional ones) for documentation and even worse, when I show my the product, I feel that my speech is disordered, inconsistant and feels low quality.

Even if, according to the feedbacks, the product in its self is great. I feel the need to learn sketching but not sure ...