Three short lines: the hyphen, the en dash, and the em dash

As a researcher, you notice details relevant to your subject of interest that others never see. What to most people was simply a dish of glass was to Alexander Fleming an indication of the power of Penicillium to stop the growth of bacteria.
Similarly, what to most casual readers are simply dashes are to careful readers distinct punctuation marks, each with its separate function. The shortest dash is the hyphen, which is also the most common. It joins two or more words to represent them as a single unit, for example, a test-tube, 4-aminobenzensulphonic acid, fail-safe, or state-of-the-art facilities. Use a hyphen – but only with non-SI units – to combine a value (number) with a noun, as in a 15-inch rod or a 2-month vacation. Note that in most such cases with only one hyphen, the part before the hyphen modifies the part after the hyphen.
Intermediate in length is the en dash; use it to indicate a range, as in 6–10 kg or 6–10 mm. In references, separate the first and last page numbers with the en dash, as in Information Design Journal 17: 153–154. In such cases, the en dash simply replaces the preposition to. The second use of the en dash is to join two words that are equal in status as it were. In other words, the first part does not modify the second part, as in Michaelis–Menten equation, energy–environment interface, and nature–nurture debate.
The third, and the longest, is the em dash, which is rarely used in scientific texts. Think of it as a counterpart of the colon (:), which comes before a list or an explanation. The em dash follows such items and either sums up their contents or introduces a contradiction, as in "Solar water heaters, wind turbines, water mills, or even a simple fire made by burning a few dried branches, all share a common feature—they all use renewable sources of energy." or "The floor was washed with disinfectant; the air was filtered through a fine filter; the surgeon used a mask and sterilized gloves—it was the food that was contaminated."