Add single vert and skin then no vertices

HI I found how to use this add on from youtuber “Keelan Jon”
He shown the tutorial which look like easy and intereting,

I try to following as his step as below
Blender Character Modeling Tutorial - Stylised Character Tutorial - Blender Tutorial - YouTube
Min 1:30 to 3:00

Add single vert> add modifier skin> but I stucked when the single vert was not shown the all vertices. It shown only 1 or 2 as following core of if instead of vertices all each edge.

Please tell me how to fix it or the way to be as on the clip.

Thank you so much,

Addon Information
Name: Extra Objects (0, 3, 7)
Author: Multiple Authors

It seems to me that this is not a review, but a question. You need to go to resources for help. And it seems to me that the site (or page) of the lesson (comment section) will be better.