Don’t confuse the hyphen (−) and the dash (—).
The Purdue Owl simply says:
Hyphens (-) are used to connect two or more words (and numbers) into a single concept, especially for building adjectives.
- The family’s money-saving measures have been helping them to build their savings.
- I had a conversation with Mrs. Skinner-Kcrycek this morning.
They are also a necessary component of the numbers 21 through 99:
- Before the exam, Tomas studied for thirty-three hours without sleep.
Dashes (—) can be used to indicate an interruption, particularly in transcribed speech:
The chemistry student began to say, “An organic solvent will only work with—” when her cell phone rang.
They can also be used as a substitute for “it is, “they are,” or similar expressions. In this way they function like colons, but are not used for lists of multiple items, and are used less frequently in formal writing situations:
- There was only one person suited to the job—Mr. Lee.
Note that dashes are double the length of hyphens. When you type two hyphens together (–), most word processors automatically combine them into a single dash.
More at Purdue Owl
Many word processing programs allow you to add a proper dash by going to the Insert tab at the top of your screen and selecting Special Characters. Many programs also allow you to specify that when you type two hyphens in a row, they will automatically transform into a proper dash symbol.
Michelle at the Waterhole gives good examples of hyphen, n-dash, and m-dash usage. Read her description of the en-dash below:
The next dash is called the en-dash (–). The en-dash is used to connect values in a range or values that are related. A useful tip to help you identify when to use the en-dash is when you’re talking about a “to” relationship (as in March to June). Examples are:
UCLA beat USC 37–10
The Stack Exchange offers a concise description below: