Punctuation

 HYPHEN ( - )
The hyphen (-) is a punctuation mark used to join words, and to separate syllables of a single word. The use of hyphens is called hyphenation. ... The hyphen should not be confused with dashes (- – — –), which are longer and have different uses.

Hyphen is used in compound nouns such as father-in-law, three-hour show, two-thirds majority etc.
Used to divide a word into syllables.
  Eg. r-e-a-s-o-n, pho-to-graph, bu-reau (బ్యూరో)

To separate parts of a compound number Eg. thirty-seven, one-half-hour.
  To form certain compound nouns.
 Eg. cease-fire, post-mortem, editor-in-chief. [But now-a-days, people do not use hyphens in
most of such cases.]

To connect the elements of a compound modifier when used before the noun, it modifies.
  Eg. hand-to-hand fight, hand-to-mouth existence, a well-known expert

To prevent possible confusion in pronunciation if the prefix results in the doubling of a letter, especially a vowel. Eg. anti - inflationary, re-election, co-ordinate, re-entry etc.
  [But, now a days, hyphen is droppped by several people.]

Certain prefixes and suffixes are used before/after the main word of a compound.
  Eg. ex-prime minister, co-pilot, self-defence, president-elect etc.,