Fix some typos, trim passive voice, tighten it up

The use of _"objects, or "left-justify" them, etc_.  struck me at first read as a little too casual. However, what I proposed isn't all that different.

The main observation is that a reader of the guide may not be in a position to actually understand what "etc." (or "and so on", for that matter) actually means in the context.  Use of such short-hands can be an issue in learning materials.