The hyphen ( - ) is a punctuation mark that is used to join words or to seperate syllables.
- This is my mother-in-law.
- One-fifth of the population was hit by famine.
- The process of de-Stalinisation is almost over in this country.
The hyphen is often confused with the dash, which is longer and has a completely different function.
The guidelines how to use the hyphen can be found here.