Hyphens (-) are used to connect two or more words (and numbers) into a single concept, especially for building adjectives. Likewise, some married people use hyphens to combine their last name with their spouse's:

• There are fewer Italian-American communities these days.
• The family’s money-saving measures have been helping them to build their savings.
• She has stopped buying 2-liter bottles and has started buying 0.5-liter bottles, instead.
• 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.

Although they can be used as substitutes for the word “to” when discussing value ranges and scores in games, it is better to use the word in formal writing situations than the punctuation:

• The high temperature will be 87-89 degrees.

Hyphens are also used in syllable breaks when words cannot fit completely on a line, and must be continued on the following line. With word processors and the ability to automatically move whole words, though, this has become less common:

• This opinion is based on sales figures for the past few months, and con-
• versations I have had with customers.

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.

They can also be used as substitutes for parentheses:

• Mr. Lee is suited to the job—he has more experience than everybody else in the department—but he has been having some difficulties at home recently, and would probably not be available.

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.
The Purdue OWL maintains a number of resources on punctuation you can visit to learn more:

• Apostrophes
• Commas
• Conquering the Comma
• Grammar and ESL Exercises
• Hyphens
• Punctuation Overview
• Quotation Marks
• Sentence Fragments
• Sentence Punctuation Patterns