This is a very powerful and flexible block allowing you to display posts using a variety of layouts and options.
Think of it as a top level index page which you can configure to point to content elsewhere on your site.
You can select what post categories should be displayed, or a specific custom post, or individual unrelated posts. Then you can select the number of columns per row and the background colour of those columns.
You can change the sort order and the number of posts per page (pagination).
You can show or hide post titles, excerpts, dates and add a link at the end of each column. And if you want, you can set that content to only appear when hovering over the post thumbnail image.
This is such a flexible block – you can either build a whole page just around this block, or drop it in amongst other blocks and use it as, say a featured posts section.
The possibilities are endless!