How to Use D's ImportC Compiler in a Program

[David T. Oxygen]

I once found that D has a ImportC compiler. It can compile C code.
How to use it?
I tried `dmd hello.c` but it didn't work. Instead,it did 
nothing,and even didn't give me an error message.
I thought the compiler was broken but when I compile a normal D 
file it can work.
I've also tried `dmd a.d b.c` and of course it didn't work too.

Who knows why? I'm waiting for your answer.