By default the blog page will show the full content of a post, but you can truncate this on the blog page using the regular WordPress “read more” feature which inserts a break in the content so the theme knows only to show that content before the break on the main blog page. This is a great way to give visitors to the main blog page a taste of your content without creating lots of duplication with the actual post itself.
If you are reading this on the main blog page you will see a link below this sentence which says “continue reading”…If you are reading this on the actual post page that link will not appear.
If you set a featured image for a given post it will appear on the main blog page immediately below the post title and meta data.