That's a tutorial (though it looks like someone posted a question as a tutorial). In theory, you can put commonly used content in them, thus not needing to write the same thing over and over again. Sort of like a sticky, but can be embedded in a post. If it's selected as a solution, both you and the author get credit.
Need to find that post and convert it to a question...
EDIT: Sorted. Now a typical forum post, though it's on the stale side.
In future, to remove them, hit the edit button. Below the edit window should be the tutorial with a cross at the top right. Click the cross, then hit Update.
To add them, use the 'Add a solution' drop-down below the post box. It only shows tutorials relevant to the current tags, so you may need to broaden them.
If you're looking to modify the tutorial adding interface, it would be nice to have the option to search through all tutorials. Sometimes the tags aren't perfectly lined up, or a thread goes on a mild tangent.
Would also be nice to have a way to change posts into tutorials; some of the stickies (e.g. the POST/video/boot issues one) could do with it.