This is a new post. Hopefully, I will do this correctly.
This fine, as far as it goes. You have an image in the text/image area, and that will appear on the post page. You need some type of Featured Image (bottom right) so that a thumnail appears on the Greg’s Training page. I’ve put a placeholder image in there to show the result. I’ve also ticked the ‘Display featured image in post lists only, hide on singular views’ box so that it appears on your page but not heading the post.
The Greg’s Training page doesn’t need to be changed unless you want to put an introductory message there. The page will automatically list posts with the Greg’s Training category allocation.
Wordpress distinguishes between Pages and Posts. Pages are usually static, displaying semi-permanent information and latest posts while Posts are standalone presentations of detailed stories, etc.
Keep going and it will all make sense soon.