What is the difference between dashes? That’s the same question I had and I found the answer here:
An en dash, roughly the width of an n, is a little longer than a hyphen. It is used for periods of time when you might otherwise use to.
The years 2001–2003
An en dash is also used in place of a hyphen when combining open compounds.
North Carolina–Virginia border
a high school–college conference
An em dash is the width of an m. Use an em dash sparingly in formal writing. In informal writing, em dashes may replace commas, semicolons, colons, and parentheses to indicate added emphasis, an interruption, or an abrupt change of thought.
You are the friend—the only friend—who offered to help me.
Never have I met such a lovely person—before you.
I pay the bills—she has all the fun.
A semicolon would be used here in formal writing.
I need three items at the store—dog food, vegetarian chili, and cheddar cheese.
Remember, a colon would be used here in formal writing.
My agreement with Fiona is clear—she teaches me French and I teach her German.
Again, a colon would work here in formal writing.
Please call my agent—Jessica Cohen—about hiring me.
Parentheses or commas would work just fine here instead of the dashes.
I wish you would—oh, never mind.
This shows an abrupt change in thought and warrants an em dash.
The rules on hyphens are too complex. There are over a dozen of them. Just go here to find the answer.