Please read (and/or buy):

1. The Elements of Typographic Style -- Robert Bringhurst

2. The Complete Manual of Typography -- James Felici

Run a search on this site for "em dash" and "em-dash," etc. There's plenty on the topic of dashes floating around here. For example: http://typophile.com/node/27727.

In addition to the suggestions made by David and Jason, you also want to look at the accepted standard of editing style for whereever you live.

Thank you, Jason!

Wikipedia has a nice explanation of the various dashes, but how you use them might vary by client, as some clients may want you to stick with certain established styles.

Thank u Jpad also..(I understand its very basic but I'm not from design background. And Not that i dont mind buying books on typography, or respect the designers here, however, someone suggested me for "a vague" suggestion here, anyone could have researched that info online but I wanted to know from the 'real designers point of view')

david hamuel: if you dont have any specific idea, then say so, dont be mr. 'ego' "read&buy this&that'

Typopo - I don't think you're being fair to David. You're new here and asking a lot of extremely basic questions (which seems epidemic these days) some of which are either repetitive (to us) or - no offense - not very interesting. While most people here are happy to help, you will find the info you need regarding type styles in a book like Bringhurst. It's a worthy investment.

You will also find - if you read the thread Jason suggested - that there isn't always a lot of consensus in the design community about even such basic matters as em and en dash usage.

Patty's right, Typopo. David was simply giving you the names of some really good manuals which, as Patty says, are worth the investment. You could also try to see if these books are at your local library, if you can't buy any books right now.

May I also suggest The Chicago Manual of Style? There is a section on punctuation which covers dashes. But as stated above, there is not always consensus on these matters, so no one manual may have the "right" answer. It is a good idea to check out more than one book.

I guess this is going to make me sound like the old fogy I am, but what is it with students today who get offended when you recommend a book to them? It is as if reading a book is a cruel imposition. Depressing.

I respect Patty's opinion and I'm truly sorry. I do appreciate everyone's help.

Actually, "I respect Patty’s opinion and I’m truly sorry — I do appreciate everyone’s help," is a good start...

I have one more resource for you Typopo: Ilene Strizver has a very recommendable and ongoing series of articles called fy(t)i -- For Your Typographic Information. The individual articles have appeared in print and online, and are now also available on her website, The Type Studio.

Cheers.