I found a built in library of actions that include an animation of an explosion. HOWEVER, the animation cant be viewed by scrubbing only by hitting control+enter to preview the movie.
?: How do I edit this object, for the size?
?: Is it possible to put a basic shape tween on this explosion so that it looks like it goes from small to large?
?: WHERE do you edit the settings for the explosion?
That probably means it's a movie clip and not a graphic. Movie clips don't play in the timeline. click on it on stage and change it from movie clip to graphic in your properties bar. Make sure to do the same for any symbols that symbol contains.