Possessive Case

Form
We add 's to singular nouns and plural nouns not ending in s. (យើងបន្ថែម 's ក្រោយនាម ដែលមិនបញ្ចប់ដោយ s)

e.g. A child's voice. Men's clothes

We use the apostrophe (') with plural nouns ending in s and names ending in s we can take 's or the apostrophe alone. (យើងបន្ថែម apostrophe ពីក្រោ​យ​ s)

e.g. the Smiths' car.

Use
We use possessive chiefly with people, animals and countries. But we can also use it (យើងប្រើ possessive ជាមួយមនុស្ស សត្វ និង ប្រទេស។ បន្តែយើងក៏ប្រើជាមួយ): We can use some noun in the possessive without a following noun when it is clear what we mmean. (ជួនកាលយើងពុំចាំបាច់ដាក់ noun ទេ), You can buy it at the chemist's (shop).
 * In time expression (ឃ្លាបញ្ជាក់កាល), A week's holiday.
 * In expression of money + worth (ក្នុងឃ្លា money + worth), A pound's worth of stamps.

With of
We use of + noun chiefly with things. (យើងប្រើ of + noun ជាមួយវត្ថុ), e.g. A key of the car.

We often say "the car key"

We use of + noun with people and animals when these are followed by a phrase or a clause. (យើងអាចប្រើ of + noun ពេលពីក្រោយវាជា ឃ្លា ឬ ប្រយោគ), I stoke the nose of a horse looking out of his stable.