of = "of" is a difficult word to explain but I will try by comparing this word "of" with some words that might exist in Mandarin.
When I look up the character 的 in my Chinese to English dictionary, the first definition is the English word "of." The second definition is apostrophe 's.
English: He is a friend of my sister.
Do you notice that in English, "friend of my sister" is written the opposite way than the same phrase 我妹妹的朋友 would be written in Mandarin?
Now what about the second definition, apostrophe 's?
English: My sister's house
How about using "of" to show direction ...
English: South of Chicago
How about using "of" to show a person being seperated from something
English: rob someone of his money
Now some Mandarin phrases don't use 的 but when translated into English, "of" would be used.
English： 1st of October
English: dress made of silk
How about I do a seperate post for the other words, "for, about & to."