We use an apostrophe and an s to indicate that person or animal owns something (oject, idea, quality). A noun with ‘s at the end shows whom the object belongs to:
Anrew’s guitar, Charles’s bike*, etc.
*We usually add ‘s even if the proper name ends in s. Exceptions are: Jesus’ disciples, and the nous ending in /iz/ sound (Jeff Bridges’ films).
Plural nouns ending in s, just add an apostrophe: the sutedns’ decision, my parents’ car, the lions’ cage.
When two or more named people share something, we put ‘s only after the last noun: I really enjoyed Angela and Andrew’s live performance last night.
When we talk about different things belonging to different people we put ‘s after each: Angela’s and Artemida’s marks were really good last term.
We also use ‘s to say when specific events happen and or how long they last:
Sunday’s trip was a disaster.
We’ve got two weeks’ break in winter.
We can also use of to show how one thing ‘belongs’ to another. When we are talking about organizations, countries and places we can use either of or ‘s:
The rules of the university are very strict. / The university’s rules are very strict.
The population of China is enormous. / China’s population is enormous.
The streets of London are very crowded. / London’s streets are very crowded.
For inanimate objects we usually use of to indicate how one thing belongs to another:
He climbed to the top of the mountain.
The teacher never forgets to give us homework at the end of the lesson.
However, in some cases where we can use of (but NOT ‘s), we can put one noun in front of the other to form a compound noun. The first noun is like an adjective qualifying the second noun. You have to be very careful as there are no easy rules to tell you which form you can use:
The corner of the street / The street corner
The results of the exam / The exam results
We also use of instead of ‘s with a long phrase:
Have you got the telephone number of the girl we met at the party?