The HYPHEN is a JOINER.
It JOINS linked words together to make HYPHENATED WORDS (Compound words)
There are not clear rules as to which words are hyphenated, but, here are a couple pointers.
Here is a GREAT explantion from GRAMMAR GIRL!
#1 – Hyphenate adjectives when they are acting like one adjective (unless you can add the word “and” betwen them)
EXAMPLE
The blue-green car
Three-week vacation
Out-of-date publications
Here we would not use a hyphen because I can add the word “and” between them.
The amazing, sensational magician
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#2 – Hyphenate Compound Numbers and Spelled-out Fractions
EXAMPLE
I have forty-three dollars
I ate one-third of the pizza
I ran the 200-yard dash
The fifty-year-old woman
Here is a couple more hyphenated words
My father-in-law
My sister-in-law
She is a know-it-all
