Compound nouns can be formed in different ways.
The most common way is to put two nouns together (noun + noun); other common types are adjective + noun and verb + noun.
noun + noun
car park Iceland shopkeeper website
adjective + noun
blackberry grandstand greenhouse small talk
verb + noun
breakwater fall-guy go-kart runway
Writing compound nouns
Many compound nouns are written as one word, but some are written with hyphens or spaces. In modern English, hyphens are less common than they were in the past. A good learner’s dictionary will tell you how each compound is usually written.
Examples of one word
bathroom sheepdog windscreen
Examples of hyphens
check-in fire-fighter son-in-law
Examples of spaces
bottle opener New Year’s Day Prime Minister
Plurals of compound nouns
We form the plural of most compounds by adding a plural ending to the last part of the compound:
We saw some large greenhouses with vegetables growing in them.
They’re building two new car parks in town.