Quoting Silence_of_Lambs:

Quote:
Maybe I'm too dumb to see it.

But where is the difference between a hyphen, an em-dash and an en-dash (except for the key-combinations) and how do I verify which to use if only one of them is present?   

The buttons are right above the overview text field... See where I boxed around in red...



As to how to tell which to use if there is only one dash there... the way I was taught in school (and also says HERE)... Compare the dash to the letters M or N in the same font (within the overview text)... if the length is closest to the "M" it is an EM dash... if it is closer to the "N" it is an EN-dash (hence the name of the dashes)... if it is even shorter it is a normal dash.

And that has been my experience with the overviews I have done (EN-dash the rare one).

That sounds a little odd to me... I always thought the school systems around here was lacking quite a bit. I was just talking to my daughter... she is a junior in high school (starting tomorrow!)... and would you believe she said that she never heard of EM-dash or EN-dash. It isn't even covered anymore. 

I wonder why we even have three+ versions of the dash.  To me, a dash is a dash is a dash (is a dash).

Short version of the dashes
1. Shortest is a hyphen...we know what that is.
2. Longest is the em dash (in printing terms the m quad)...approximately the width of the lowercase m in a particular typeface...different lengths between regular and condensed typefaces, etc.
3. Middle is the en dash (in printing terms the n or nut quad)...approximately half the width of the em dash or the width of the lowercase n.
Note: em is longest, en is about half the width of the em and hyphen is about half the width of the en. Specialty typefaces sometimes do not follow these specs.

Just like everything else in grammar... yes they do have their own meanings. Unfortunately they aren't always used correctly in the overviews. But that is normal.

As been said before...

Dash: Combine Word (advanced-level; well-being; long-winded)
EN-Dash: Show Through... such as a timeline... (July 9–August 17; pp. 37–59)
EM-Dash: Create a Strong Break (Key events in Lex and Clark's respective histories come to the forefront when each — Lex willingly and Clark unwillingly — undergoes a risky Summerholt Institute memory-recovery treatment.) This last example has EM-Dash and normal dash used correctly.

So as you see... each do have their correct usage. Of course for our purposes per Rules we use whichever is used on the cover... whether it is correctly used or not.

Well, with all the talk about school, I have definitely learned from my teacher(s) that the en-dash [alt+0150] (Swedish tankstreck – not very different from German Gendankenstrich), is the most commonly used (aside from the regular hyphen). We simply don't use or even know of a third (em-dash) hyphen, as it's not really necessary to have that many.
Not for us.
That's why I think there are different standards in the world and why there must be some international standard. At least it would make things easier. I bet your kids today learn about the longer hyphen too, the en-dash. I hadn't heard of em-dash until I visited this site. So to me, it's either something obsolete, or an American thing.

Hence why I am just surprised to see them used, at all.
And what i cynically meant with that we all don't live in the US, is the mentality that everything you do, we should do as well. So I'm happy not to. But, yeah, that is off topic and all that. Unless you start giving me that mentality here.

Lastly, Addicted2DVD, you totally contradict yourself and what you write as a description of use, when you use en-dashes where there must be hyphens. It's like your re-writing the grammar.
Hyphen is often used, that's why it's so conveniently put on any keyboard: -.
For the more unusual en-dash, you need to access it in a writing program as it is mostly used in more "important" situations rather than every-day-life situations. Or you need to know the alt+0150 command, I guess.

Regardless of which, it would definitely not be appropriate just because some think that the em-dash "rules", to substitute the en-dash with them. When I look at text I compare the lengths of the hyphens, I don't go by some odd rules I've (personally) never heard of.

And, Addicted2DVD, while you in THIS case with the Smallville season 3 overview may be correct about the em-dash, it's not something I would accept much further for other titles in my collection. The em-dash has to be at least twice as long as the hyphen to be an em-dash, to me.
In the overview that you are submitting, the "other hyphen" is just slightly shorter than twice the length of the regular hyphens. But the em-dash you are using is three times as long...
That's simply not how it looks in the overview for the title...!
Comparison:
-
– Looks like about 2x the length
— 3x longer or more than the hyphen
This is what I see in the overview when studying it in detail.
And I honestly don't care much about American grammar, that apparently isn't even taught in schools today.
To me, the em-dash issue is a DVD Profiler virus.

I point again to my uploaded image.

You all determine from this – what you see and what you would contribute.
ASIDE from some odd "grammar rules"... That aren't even relevant to DVD Profiler and our system!
It's more like a Besserwisser attitude, to me.