Can someone give me an example I can understand? Right now I'm using K2 v2.6.7. Under K2 Parameters I went to the content tab. In that section they have Content Cleanup.

I'm assuming this will allow me to hide html or other code that I don't want users to see if I share it to a social network. For instance, one of my post I use to display a photo gallery starts with {gallery}12345{/gallery}

I shows the first image of the gallery (what I want it to do) but I don't want the html information seen if I share the article to Facebook. So what do I have to do to hide this? Right now in that version it doesn't seem to even work. I save my choice and it acts as if it's saved but when the screen returns nothing is there. Might be a bug.

Which version of Joomla! are you using?

By default K2 will send Facebook the K2 image, if that image is not in the correct dimensions ( at least 200px x 200px) then the first suitable image will be used instead.