Confusion about featured posts

Hello. Please excuse me if this has been answered a few thousand times. I may be searching the wrong tag words or using incorrect terminology.

Are the front page images under the slider that link to blog posts called “Featured” images or posts? For the life of me, I cannot grasp how certain blog posts of mine show up there and others won’t show up regardless of what I do. Is this category linked? I’ve tried that, but no go.

All I want is to be able to checkmark a category (call it featured-posts) that tells WP/Customizr that this post goes on the front page. I can’t figure it out. Been trying and searching for hours. Or perhaps, I’m missing a checkmark somewhere that does this outside of categories?

I know I have to set a “Featured Image” on the blog post’s Edit page. Done that. I swear I can create two identical posts and one will work the way I want and the other won’t show up. I know I’m doing something wrong, but what it is I don’t know.

Finally, on Customize->Front Page Content->Set the number of posts to display here, if I set this number to 6, I get 6. If I set it to 9 I get 6. Is this a limitation of the free version?

Thank you all for taking the time to read this and hopefully help me with this. It’s most likely very simple, and due to user error. I acknowledge that.

Dave in Trinity