Hello everyone,

I am confused about the usage of "of". Is there a quick tutorial that I can read about it? For example

could you tell me if there's a difference between these following sentences?

1) Department of Domestic Security

2) Domestic Security Department


3) The language of conversation

4) The conversation language

how about this?

5) No matter you level of proficiency ...

6) No matter you profeciency level ...

So, is there a rule?

Thanks in advance.
I don't know of a rule, and I don't know of a tutorial.

Often the choice between such phrases is made on the basis of how it sounds within the sentence where it occurs. It is often a matter of style and context whether you use, for example, level of proficiency or proficiency level.

There is no essential difference.

proficiency level......... Adjective+noun

level of proficiency ....... noun + prepositional phrase
 CalifJim's reply was promoted to an answer.