blog posts featured image not working + post disappears

Hi I really like this theme! But, I am new to wp and trying to figure out some stuff.
First, I set the featured image for my first article but on the homepage it shows the full article, where I thought it would have shown only a few lines of it. How do I do that?
Then it has happened now twice that when I visit the website the article is not there, both in the homepage and in the blog. This morning logging in my wp back page I updated the article and it did show on the website. But then, when I logged out and then back in, article disappeared again.
How can I fix this?

To show only excerpt on homepage/blog page you should enable Excerpts (text summary). This can be done via Appearance - Theme Options - Main - Home Page Settings - Display excerpt for each post.

For second part of your problem I really don’t have a solution. In theory it is not even possible unless you erased/ didn’t publish it properly. Hit preview but not publish or set it to private. Or some other thing.

This problem can’t be theme related because WordPress itself handles, posts, images, pages etc but theme only applies styles to it. If there is post on WordPress dashboard and it it set as published, it will be displayed no matter what.