Hello, Sun Kunawattanakorn!
Obviously, you looking in a wrong place.
The Vision Portfolio menu should be in your Dashboard, on the top-left corner.
https://prnt.sc/gl2fxu
If you don’t have it,
you need first install and activate required plugin named “Vision Core”
and register your theme.
Then your portfolio menu will appear.
To do that, please follow the guide below:
Product Registration
Next, when you find the Vision Portfolio menu, you can setup the portfolio page.
please check the guide below:
http://docs.theme-vision.com/article/setup-a-portfolio-page/
Best Regards