In English, sometimes we use a noun like an adjective. A noun can be used before another noun, in order to give more information about the 2nd noun. Here are some examples from the listening lesson “Stars on Ice“:

figure skating
a figure skating tour
world-class figure skaters
a heart attack
four-time world champion

Two (or more) nouns used together are a type of compound noun.

Some more examples:

a bus driver
a paper bag / a plastic bag
chocolate milk ( = a type of milk)
milk chocolate ( = a type of chocolate)
ice cream
a hotel room
a parking lot
a lottery ticket
My 5-year-old son
a computer part
police officer

Let’s look at car accident. The noun car gives more information about what type of accident it was. 

INCORRECT:
an accident of the car
a car’s accident
an accident car

ALWAYS REMEMBER: in English, the adjective comes first [including a noun that acts like an adjective!]

There is no rule to memorize here. These are word combinations [collocations] that need to be memorized. There is no book or list you can look at to memorize them all. You learn them by doing as much reading and listening in English as possible.

NOTES:

*When numbers are used as an adjective, (time, age, etc.), remember to use a hyphen:

My son is 5 years old.
My 5-year-old son starts kindergarten this year.

Kurt Browning won the World Championships four times.
Four-time World Champion Kurt Browning performed a routine in hockey skates.

*A compound noun is very different from a possessive noun:

Cheryl’s car = the car belongs to Cheryl. It is her possession.

Cheryl was in a car accident. = Cheryl was in an accident. Adding ‘car’ gives more information about what kind of accident she was in.