Posting the main url of drupal site on facebook wall When pasting the URL of the Drupal site in question as a facebook message, the message, title and image that are being fetched from that drupal site are not the ones that are supposed to come up.
From what I gather, Facebook module and OpenGraph stuff seems needed in order to figure this out which seems overkill for this problem...

The homepage of the Drupal site is a view with some blocks in the sidebars. When you paste the URL of the site (www.mysite.com) in a facebook message, it fetches some text out of a block, and an image from some other node. Instead, I want to be able to choose which text it fetches from the site.

The answer to this question How to change facebook og:image to post image link? seems to come close and is telling me I need to use the metatag module. It doesn't explain how to go about it, but I installed the module and changed some of the values in the configuration, but didn't have any effect. Also flushed caches many times. 

Also installed the fb module, I read the README.txt from the fbmodule from the beginning until the end (as asked).

I have a feeling like I don't necessarily have to get a degree in the the huge Facebook API/Opengraph rabbithole in order to get this sorted, do I? 
I mean, there has to be one place where you can just determine when the text, image and title should be on the wall without too much of a huge construction around, no?
You have a two part question here.

One, the best way to deal with OG info on your site is with the Metatag module:


  The Metatag module allows you to automatically provide structured
  metadata, aka "meta tags", about a website. In the context of search
  engine optimization, when people refer to meta tags they are usually
  referring to the meta description tag and the meta keywords tag that
  may help improve the rankings and display of a site in search engine
  results. In addition, the module provides support for meta tags (Open
  Graph Protocol from Facebook, Twitter Cards from Twitter) that allow
  control of how content appears when shared on social networks.


When you install and enable this, you can customize what OG info appears where, and it has full token support for dynamically creating the meta elements pages on a page's content.  You can also hardcode values for specific cases, like the home page.

The second part of your question has to with the fact that FB heavily caches page contents.  The provide a debug tool for dealing with this:

https://developers.facebook.com/tools/debug/

In addition to seeing exactly what OG info it is pulling in about a URL you provide, it has the side effect of clearing the cache for that particular URL.