where is post thumbnail?

WP Version?

3.0.1
(Why does it ask me this when I post if it doesn’t display it?)

FYI, the theme I use does not natively support post thumbnails, but I added all the codes from this article: https://markjaquith.wordpress.com/2009/12/23/new-in-wordpress-2-9-post-thumbnail-images/

activate “add_theme_support( ‘post-thumbnails’ );”. Then you will get a “feature thumbnail” box at left panel.

follow this link https://www.wpbeginner.com/wp-themes/how-to-add-post-thumbnails-in-wordpress/

Yes, I think you are not understanding me. I have done all that.
Lemme try again.

In my blog (single post) I want to have a large-ish picture on the right hand side, beside my first paragraph.

On the main page (index) I want it to show the first paragraph and the thumbnail on the right side, but I want it to not show the large-ish picture.

Doing it as instructed in the above tutorial ends up showing the large picture and the thumbnail on the main (index) page.

How can I make the main (index) page show only the thumbnail and no other pictures from the blog (single post)?

Thanks!

Examples:
How I want it to work: https://mmajunkie.com/
How it works for me: https://mmaviewers.com/TestingGround/ ??