Correct usage

[JustAlilBit]

Hello all,
What's correct usage of word "of" ?
Do we use "of" when we want to express that something is someone?
For example -> The king of kings.

When do we use ( 's - is )?
Of course we use when we abbregviate something. For example: Tom's cat.
Sometimes I cannot express possestions of someting. I think teachers will get what I am trying to say. I hope that teachers will try express me correct usage of this two things. Sometimes I feel that I need to use them, but I am not sure that I need use it or not.

[SoothingDave]

Budweiser is the King of Beers. That describes the type of king it is. Among all the beers, it is the king.

That is one way to use "of."

Possession is usually described as you say: Tom's cat.

Do not confuse the "'s" of possession with the "'s" of a contracted "is."

There is Tom's cat (possession). Tom's a good guy. (Tom is)