When to use "-"? Please explain the function of "-" in this sentence.?

Like em dashes, en dashes can be used instead of colons, or pairs of commas that mark off a nested clause or phrase. They can also be used around parenthetical statements – such as this one – in place of the em dashes preferred by some publishers, particularly where short columns are used, since em dashes can look awkward at the end of a line.