Hi there,
To display the posts in columns, use the following code in your template files: <?php do_action('columnpost'); ?>.
You can use the shortcode [columnpost] in your page or post.
Also, the column posts can be displayed in the sidebar by using the Column Posts widget.
Answer to your questions:
1. In the Wordpress dashboard, go to settings/Column Posts
2. To display Thumbnails, go to Posts section and check show thumbnails.
3. Go to Columns section and click on Three number of columns.
Kind regards,
Lebasca